I have just ported my Tata Docomo number into BSNL Mobile and it is working good. But I am not able to check my balance and recharge top up coupons because USSD code that we run, like
*123#, are not working. It says "Connection problem or invalid MMI code".
Unfortunately, it is happening only in my Samsung Galaxy Y Duos GT-S6102 which is based Android 2.3.6 Gingerbread. I tried on another cell phone and there was no error. Talktime balance showed up and even I recharged with the top up coupon.
My phone has dual SIM support and there is no corruption on both SIM ports. Message centre number for BSNL mobile is also correct and I am able to send SMS too. There was no problem with Tata Docomo either.
Don't know what's the problem with MMI codes.