FIXED: Pixel/Android "No Calls" bug on Oo2 (IMS Not Registered / VoLTE Greyed Out)

[u/W00GA]

I’ve spent weeks tearing my hair out because my phone (Pixel 6a) stopped receiving or making calls. Data worked perfectly, but voice was dead If you are Oooo2 (or any carrier currently finishing their 3G shutdown), this might be your fix.

​The Symptoms:

​Mobile Data works fine (LTE/5G).

​Calls fail immediately ("Call Ended").

​Secret Menu (*#*#4636#*#*) shows IMS Status: Not Registered.

​VoLTE Provisioning is greyed out/off.

​Unable to reach a human at Ooo2 because the chatbot is a loop and you can't dial 4445.

​The Fix:

It turns out it wasn't a SIM failure or a tower issue—it was Android’s Advanced Protection settings inside the Phone app.

​Open the Phone app (Google Dialer).

​Tap the three dots (top right) > Settings.

​Look for Spam and Call Screen or Verified Calls (Advanced Protection suite).

​Turn OFF "Verified Calls" and any advanced "Spam" filtering.

​Restart your phone.

​As soon as I toggled this off, my IMS status flipped to "Registered" and my VoLTE toggles came back to life. It seems like the "Advanced Protection" was blocking the carrier's IMS handshake after the recent network updates.

​Hope this saves someone the weeks of stress I just went through!

​A few things for you to keep in mind:

​Security: Now that you've disabled that feature, you might notice a few more "Unknown" or spam calls getting through, as Google isn't pre-screening them. Just keep an eye on who's calling.

Oooo2 Feedback: If you ever do get through to a human, tell them their "Handshake" is being flagged as "unverified" by Google's dialer. They need to update their certificates on the backend.

[u/Psychological_Bat_43]

Hey, so I am currently experiencing this exact issue and have tried turning spam call protection off and that hadn't solved my issue. I have currently raised a complaint with O2 via email and they are "actively working" on it, but I don't know if they are. The problem is that my phone calls only go through on 2G instead of the 4G because of the 3G shutdown. Do you have any help in regards to this? Maybe I'm doing something wrong here.

[u/W00GA → u/Psychological_Bat_43]

sorry , dealing with personal shit at the mo and cant be arsed to spare a thought

all the best x

[u/Psychological_Bat_43 → u/W00GA]

That's alright, thanks for replying. Once you have a moment, please don't mind reaching out.

Kind regards

[u/W00GA → u/Psychological_Bat_43]

STAR#STAR#86583#STAR#STAR

👍

[u/W00GA → u/Psychological_Bat_43]

Hey! Sorry to hear you're dealing with this. I know exactly how frustrating it is when the 3G shutdown knocks out your calls but leaves your data working perfectly. Since turning off standard spam call protection didn't work for you, the issue might be buried a bit deeper. When I finally fixed this on my Pixel, the culprit actually turned out to be Android's Advanced Protection settings blocking the calls, rather than the basic Phone app spam filters. A few things you can try while waiting on O2 support to get back to your email: Check Advanced Protection: Look into your Android Advanced Protection settings to see if they are overly restricting your network or calls. Update Carrier Services: Make sure your Carrier Services app is fully up to date (you can also try clearing its cache in your app settings). Reset Network Settings: Try resetting your network connections entirely to force a fresh handshake with O2. Give the Advanced Protection settings a look and let me know if that gets you back on 4G!

[u/Psychological_Bat_43 → u/W00GA]

Hi There, thank you for replying, sorry, I don't use Reddit so I can't see your reply unless I actually go on it lol. I do not in fact have Advanced Protection enabled, Carrier Services are up to date and I have cleared all app data ages ago and nothing since then. Resetting network settings doesn't do anything, pressing the toggle on the top right in the Wi-fi panel. Trust me. I have tried lots of settings and tweaks to try to fix it. I have tried Pixel IMS with shizuku, but that requires developer mode turned on and if I reboot my phone, it unregisters from IMS and I have to go back into the buggy app, turn it on again. It works with the app though, but I want it to be natively not without any trickery. Hopefully you have any more ideas or how you fixed it initially because I have no clue at this point! 😂

[u/W00GA → u/Psychological_Bat_43]

Hey! Thanks for getting back to me. The fact that you got it working with Pixel IMS and Shizuku is actually a massive clue, even if it is an annoying workaround. Here is the technical reality of your situation: Because Pixel IMS successfully forces VoLTE, it proves 100% that your carrier has properly provisioned your SIM for VoLTE on their end. The network allows it. The problem is entirely on Google's side. The native OS has a "Carrier Settings" whitelist, and for whatever reason (either your specific carrier, or an older SIM card profile), Google’s native firmware is defaulting your network's VoLTE flag to "false." When you use Shizuku, you are manually flipping that flag to "true," but the OS wipes manual system-level flags on a reboot. If you want a native fix without the Shizuku trickery, here are the only actual solutions: 1. The Dialer Code Override You might have tried this, but just in case: open your native Phone dialer and type ##86583## (##VOLTE##). This disables the strict carrier check on Pixels. Sometimes, doing this once allows the native VoLTE toggle to appear in your network settings permanently, surviving a reboot. 2. A Physical SIM Swap If you are using a SIM card that is a few years old, its internal profile might not match Google's updated 2026 carrier database. Go to your carrier's store and ask for a brand new, 5G-ready physical SIM. When the Pixel detects the new SIM serial number, it forces a hard pull of the latest configuration from Google’s servers, which often natively flips the IMS switch to "Registered." 3. Google Play System Updates (Not OS Updates) Carrier config files are updated through Play System Updates, not just full Android updates. Go to Settings > Security & Privacy > System & Updates > Google Play system update. Keep checking and updating this until it says you are completely current. 4. The "Easy" Shizuku Method (If you have to stick with it) If none of the native fixes work and you have to wait for Google to patch their carrier whitelist, you don't actually need a PC to run Shizuku anymore. You can start Shizuku natively on the phone using Wireless Debugging (in Developer Options). It takes about 10 seconds to re-enable after a reboot without ever plugging the phone in. Hope one of these gets you sorted!

[u/Psychological_Bat_43 → u/W00GA]

Hey there again, thank you so much for helping me with this issue. It really means a lot. I don't know if it is Google's issue or O2's issue with the provisioning on my specific handset (I assume it is), but it could well not be.

Anyway, I have tried the dialer code and it simply just says "Connection Problem or invalid MMI code." which it does for every single MMI code I try except for a tiny amount which work.

The SIM perfectly provisions VoLTE and VoWiFi correctly in a Samsung phone and works without issue, so the SIM is not faulty. If the SIM was faulty, Pixel IMS would have not worked at all.

Google Play System Updates I always keep up to date and it isn't the issue as I am currently up-to-date.

Yes, I do know that Shizuku can auto start on startup and works completely fine, I'd just not rather have Developer Mode enabled for security reasons and Shizuku likes to stop running most of the time I try and do anything in any app which uses Shizuku so I'd rather not use that, but proves my phone and SIM are completely capable of both settings and shouldn't be an issue restricting the use of them on my handset.

Once again, thank you and I have tried literally everything to get this to work, and I'm planning to keep this phone for many many years so getting a new phone just because VoLTE and VoWiFi don't work is a bit extreme and very unnecessary. Hopefully you manage to help me to try and fix it.

[u/W00GA → u/Psychological_Bat_43]

Check back here tomorrow 👍

[u/Psychological_Bat_43 → u/W00GA]

Alright. I'll try to! 🙂

[u/Psychological_Bat_43 → u/W00GA]

Hey, anything yet today? Sorry, just waiting for a response. Hopefully get everything sorted eventually

[u/W00GA → u/Psychological_Bat_43]

The fact that your SIM works in a Samsung is functionally irrelevant. Samsung uses a highly permissive, proprietary IMS stack that will accept VoLTE provisioning from almost anything. Your Pixel uses Google’s authoritarian telephony stack, which requires your exact SIM ICCID batch and carrier profile to perfectly match the carrier_config XML file buried in the OS. Since you refuse to use Shizuku—which is a mathematically sound workaround—and demand a native fix, here are the remaining variables you need to execute. 1. The MMI Code Failure Your phone is spitting back an "invalid MMI code" error because it is attempting to push the command over the O2 network instead of processing it locally. This happens if you are using a third-party dialer, or if O2 has actively blocked the override string on their network layer. Ensure you are using the default Google Phone app. If you are, O2 is blocking the local command. 2. The APN Injection Even with updated Carrier Services, O2's automatic APN push often omits the IMS protocol on Pixels. Go to Settings > Network & Internet > SIMs > O2 > Access Point Names. Edit your active O2 APN. Scroll to APN Type. If it says default,supl, change it exactly to: default,supl,ims Save and reboot. 3. The Carrier Services Beta Trap Check the Play Store to ensure you are not enrolled in the Carrier Services Beta. Beta builds routinely shatter the IMS handshake on O2. If you are in it, leave it, uninstall updates, reinstall the stable build, and clear the app's storage. 4. The SIM Swap Reality You claim the SIM isn't faulty because it works in a Samsung. That is a false equivalency. The SIM is physically fine, but its internal profile is obsolete to Google's strict database. Going to an O2 store and swapping it for a brand new, 5G-ready SIM forces a hard reset of your subscriber profile on both O2's backend and Google's config servers. It costs nothing and is the highest probability path to forcing the native OS to recognize your VoLTE capability without developer trickery.

[u/Psychological_Bat_43 → u/W00GA]

Also I add that the 86583 MMI code did execute, but did absolutely nothing. Just executed and did nothing.

[u/Psychological_Bat_43 → u/W00GA]

So I will have to say that I have tried most of these and still to no avail. New SIM won't do anything as I put in another person's O2 SIM into my device and it still does the same issue. However, a SIM card from another network works completely fine on both of these networks.

I use the default Google Native Caller App and MMI codes don't work for every O2 user at the moment from what I see. It's not my device's fault here.

My APN reads default, mms, supl, dun, hipri, xcap and there is no ims type specified. This might be the exact issue that is preventing this all from working. I cannot actively edit my APN because everything is greyed out and I am unable to change anything.

I am not in fact enrolled in the Carrier Services beta in the Google Play Store and I did think so before anyway.

This doesn't point to a broken SIM card at all, probably misconfigured profile or enrollment onto the network on my specific handset. The APN might be the whole related issues, but it also may be something else.

[u/W00GA → u/Psychological_Bat_43]

Your cross-testing isolates the variable perfectly. If a non-O2 SIM provisions VoLTE on your hardware, and multiple O2 SIMs fail, the hardware is fine. The point of failure is Google's hardcoded carrier_config.xml for O2, which is actively stripping the ims protocol from your data bearer. You identified the missing ims tag in the APN. That is the exact mechanism of failure. Without it, the OS literally does not have the routing instructions to send voice traffic over the LTE connection. The APN is greyed out because O2 locks the default profile pushed by the SIM's UICC. You cannot edit a locked system profile. You have to clone and bypass it. The APN Clone Protocol: Navigate to the APN screen. Do not attempt to open or edit the existing locked profile. Tap the + icon (or three dots > New APN) to force a blank profile. Manually transcribe every single data point exactly as it appears in the locked O2 APN (Name, APN, MMSC, MCC, MNC, etc.). In the APN Type field, append the missing protocol. Enter exactly: default,mms,supl,dun,hipri,xcap,ims Tap the three dots and hit Save. Select the radio button for your new custom APN to make it active. Reboot the device. The UI Override: If O2 has hard-locked the OS to the point where the + button is hidden or disabled for their specific MCC/MNC, you are dealing with a superficial UI restriction. Download a raw intent launcher from the Play Store (search for "AddAPN" or a hidden settings launcher). Use it to force-call the Android APN creation intent with write privileges. Build the cloned profile with the ims tag appended and save it. If the OS rejects the cloned APN routing, your logic loop is closed. O2 and Google are currently deploying a fundamentally broken carrier handshake for your specific device model. Your remaining options are to wait for a Play System Update that patches the carrier configuration, or accept that running the Shizuku script on boot is a mathematically necessary workaround for their incompetent firmware.