KEY2 call forwarding error on AT&T
Sometime in the past 4 months, my Key2 stopped being able to configure call forwarding using either the standard **004 USSD/MMI feature code or using the Phone app's settings menu (Phone > Settings > Calls > Call forwarding > Voice).
When I try using the **004 feature code, I get the following error every time: "Call forwarding: Connection problem or invalid MMI code."
When I try using the Phone app's settings menu, I get the following error: "Call settings error: Network or SIM card error."
I initially thought this was an AT&T carrier-related issue, but today AT&T Tech Support asked me to try moving my SIM card into a different model of Android cell phone. To my surprise, it turns out that call forwarding configuration works just fine on that other phone using the same **004 USSD/MMI code! This appears to be specific to my Key2. AT&T has confirmed that there is no issue on their end.
Another odd thing is that it used to work on my Key2 on the same carrier. I am certain that I set up conditional call forwarding last year on my Key2 using the **004 feature code. I only noticed it is no longer working when I tried to change my forwarding number last month.
I have triple-checked that I am using the proper USSD/MMI feature code sequence, **004*1xxxyyyzzzz#[SEND], where xxxyyyzzzz is the target phone number). I have already tried using different target phone numbers; that is not the problem. And, I have tried using various other USSD/MMI feature codes (**21, **67, *004, #004, **002, etc.), and none of them seem to work on the Key2.
Any idea what is going on? Has anyone else had this issue with the Key2 on AT&T or another GSM carrier?