The MSISDN is already registered to another IAM user account

stefanoforesti wrote:

this is how in stumbled in the fix

 

logout of your existing tmobile email account 

 

signup for a new account in t-mobile.com with your new **tmobile phone number** not an email address

in the signup you are asked an email address:  put the email address of your old tmobile email account, and its password

now you are asked if you want to manage multiple accounts from that email:  reply yes

go through verification codes both in email and phone

now you are in your old email account that has the new phone number

 

Stefano

I had the exact issue. I followed your steps and it worked. I am now able to log back into my account. Thanks a bunch!