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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.

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Can you try having only BSNL SIM in your phone - just to isolate the problem? My suspicion is that USSD code that are to be sent through the other SIM. – Narayanan Dec 27 '12 at 11:01
@Narayanan I tried as you said. But failed again. I don't think that would be the issue as BSNL is the selection. – user12288 Dec 27 '12 at 12:49
@iKrshnan As a last resort, try factory reseting the phone. You should backup the contacts, files and apps first. – VedVals Jan 13 '13 at 18:44
Thank you Narayanan and VedVals for your comments. After trying in many ways but could not find the solution and neither the reason. When I put this SIM card in other phones and put other BSNL SIM card in my phone, there is no problem. USSD/MMI codes are working. Only my BSNL SIM card has the problem in my phone. Well, I decided to use it like this. I cannot recharge or do other USSD/MMI code stuffs in my phone and it's ok for now. :) :( – user12288 Feb 17 '13 at 13:51

Exchange the SIM cards with two different handsets and replace it as earlier. This worked for me.

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