Fix T-Mobile + Google Voice Voicemail "call forwarding connection problem or invalid mmi code" Problem

Fix T-Mobile + Google Voice Voicemail "call forwarding connection problem or invalid mmi code" Problem

You love your Android on T-Mobile, but hate the T-Mobile Visual Voicemail App. You love Google Voice, but can't seem to get it working. Thankfully, I have a good explanation for you and solution! For whatever reason, the instructions Google Voice provides you don't work and when you do try them you get this error:

“call forwarding connection problem or invalid mmi code”


It sucks. I know. I've been there and I've also solved it!

First the ‘why'. If you want to get straight to the solution, scroll down. 🙂

Why activating Google Voice Voicemail on your T-Mobile line can possibly fail:

  1. A T-Mobile prepaid plan (like FlexPay) will NOT WORK. Don't even try. Don't bother. All documentation says it won't work. I've seen people who have played around with setting to get it to work, but in general it won't. If you are on pre-paid, this article isn't for you.
  2. Your plan does not support certain ways of changing plan settings (such as call forwarding options).
  3. You entered in the wrong info (happened to me twice!); more on this in the solution section.

My guess is, if you are getting the ‘invalid mmi code' screen when you try to enter in the Google Voice's ‘active voicemail' code into your phone, you are doing it correctly … it's just your phone plan that doesn't support that ‘code'.

Let me make a few assumptions here first:

  1. You already have the Google Voice app installed on your phone.
  2. You already have a Google Voice account setup and ready.
  3. All that's left is to ‘activate' the Google Voicemail on your phone and through the website.

Big Note: you must also activate Voicemail through the website! This step is NOT optional. 


The solution:

Whether you are getting the annoying “invalid mmi code” Or “your provider doesn't support changing call forwarding” error messages, the steps below should pretty much fix it.

For most of us, the problem arose when we tried Googles steps of “Enter the following code into your phone and press dial” and you had to enter something like “*004*<your GV call in number>”.

There is something very very important I need to tell you first:

  • If you enabled Google Voice first directly from your phone (ie: never went to the website, and only installed and tried to use the Android App): you need to go to the website to get your activate code thingy. What is the activation code? It starts with *004* …. but DO NOT USE IT. Because it will not work. Also it most likely provides you with the wrong number anyway.

To go around this, head directly to and log in. If a screen pops up asking you to activate your voicemail, ignore it. If you cannot ignore it, try clicking though until you're able to manually get to the settings.

So click on the Gear icon in the top right, and go to Settings. There, if voicemail is activated: DE-ACTIVATE the voicemail.

Now, click on Activate. It will pop up with a rather nice and handy CORRECT phone number for you to use. What is the number? In the pop-up screen you'll get something like:


Of course, that is a fake number that I put; You will see your Google Voice voicemail number. Write that number (the one that starts with 1, and ends right before the #) down where you have it handy.

Now go to your phone, because it's time to get this solved! Google Voice App installed? Check. GV Account ready? Check. Open up your phone and get to the phone dialer settings.

For me, to get there I had to open the phone dialer, then press the menu button on the phone and then click on Settings. Once in there, there are one big thing to take care of: Voicemail. And after that, some custom settings!

First Voicemail: Click on that setting and make sure “Google Voice” is selected as your Voicemail provider. If you get an error message about not being able to retrieve current settings, that's ok. Ignore and continue on.

Now head back to the phone dialer. Because it's here that we will enter some code/numbers and dial them in-order to edit our call forwarding options!

Why do we need call forwarding? Because it's call forwarding that ‘forwards' the calls to the voicemail provider when we do not pick up (or are busy, or ignore them).

There are THREE settings to dial.

  1. Call forwarding if no reply.
  2. Call forwarding if busy.
  3. Call forwarding if not reachable.

First, make sure your WIFI is disabled on the phone (because WIFI dialing makes things messy here). Then Enter these three commands into your phone, one at a time and pressing the call/dial button after each one:

  1. **61*yourGVinNumber#
  2. **62*yourGVinNumber#
  3. **67*yourGVinNumber#

61 is for CF if no reply, 62 is for ‘if not reachable' and 67 is the ‘if busy' setting.

This will set your proper call forwarding options and will make your line properly use Google Voice.