I'm on Verizon in the US, and Verizon doesn't use USSD, so I can't really test anything. I've seen the problem when I've travelled, but can't offer a solution.

Some of these apps might get around the problem.

At this time, it is doubtful that anyone is doing enough work on this phone to find a solution. The user Doctoror is our main developer here, and I believe his provider does not use USSD either.

This thread has more info on the problem:

http://androidforums.com/threads/rom-stock-jelly-bean-4-1-2-m040.803260/

 

Read this about USSD codes on this phone:

http://androidforums.com/threads/rom-stock-jelly-bean-4-1-2-m040.803260/page-4#post-6381908

 

Yes, there were no USSD problems with M020. This problem was introduced in M040.
Unfortunately the USSD problem is not currently solved by anyone. I'm afraid I'm not working on it and not investigating this issue further. I found my way around not using USSD at all. My provider supplies an app in Google Play which does all stuff that you could do via USSD.

 

I have a proplem like this, can't fix this ???

 

I think proplem at setting on "Reference country setting", touch then error "unfortunately ...", if fix this here, I think everything ok.Oh my Rom use Nextlaucher and theme of them,

 

Who can fix this proplem ?

 

http://androidforums.com/conversations/casio-c811-4g-ussd-fix-solution.741518/
Thank "TheDriver"
There is a problem with USSD responses with some foreign languages (others than English).
Device doesn't handle some encodings correctly and and shows a bunch of unreadable symbols.
The only man, I know, who have explored USSD problem is liver87 from 4pda. He've turned the device into the modem mode, then used an external program to send/receive USSD's from the PC.
He stated responses was shown correctly which points to the modem FW is working OK. The problem is located somewhere in dialer and/or its related resources (e.g. telephony service etc.). If this is the truth someone can decompile the dialer (other apk's) find the place USSD's are being decoded and fix it.

You can read original post in Russian here:
http://4pda.ru/forum/index.php?showtopic=497930&view=findpost&p=51585327
Translate with Google translator.
You can contact liver87 to ask some details. He's from Ukraine and I don't know does he speak English freely.
I should remember, I do NOT have Casio device on my hands and never had, so I can't debug this problem.

 

If you use ussd to check balance you can use sim toolkit to check(it worked for me in my country - Viet Nam)

 

Try this app by Bitdefender, it's free and just for the issue you mentioned
https://play.google.com/store/apps/details?id=com.bitdefender.ussdstopper

 

i'll try, and not fix it ;(

 

Hello everyone, I have tried to fix this error. I finally succeeded. You can download the file Phone.apk that was recompiled. Just put your phone into airplane mode, copy Phone.apk into /system/app on your phone. After that set permission for it to rw-r--r-- and restart your phone. I have test it on my c811 android 4.1.2, it 's ok. I will write instructions step by step how to fix this error step by step when i have free time
***Note: remember backup your old Phone.apk and Phone.odex (if you have not deodex Phone.apk) in case of it 's failure.
Link download here: http://www.mediafire.com/file/ddvx9gi2cvo0ril/Phone.apk


Vietnamese: Xin chào các bạn, trong thời gian mình sử dụng casio c811 android 4.1.2, mặc dù gặp 1 vài vấn đề nhỏ nhưng mình cũng đã cố gắng tìm cách khắc phục, và hôm nay mình đã rất vui vì đã sửa được lỗi encode sai ussd, lỗi này cũng khá khó chịu. Các bạn chỉ việc bật chế độ máy bay trên điện thoại, copy file Phone.apk đã chỉnh sửa vào /system/app, khởi động lại máy và hưởng thụ
**Chú ý: Các bạn nhớ backup file Phone.apk cũ và Phone.odex trước khi copy file Phone.apk mới vào phòng trường hợp có lỗi thì lấy lại file cũ. Mình sẽ viết lại từng bước làm thế nào để sửa lỗi này khi nào mình có thời gian rảnh.

 

It's traditional characters, so not from mainland China, but it doesn't make any sense to me. It's like something a spambot would do, basically gibberish.

 

it was error when decode characters that were encoded in utf-16LE, i have fix it by modify system app: Phone.apk. Characters, It's like Chinese but not