I bought a Galaxy S3 mini from Amazon about two months ago and was shipped with an international version around $230. First thing I did was using the same mini Sim card that I used on other phones for many years; Since it worked on last 3 regular cell phones with no problem. After that my phones was intermitted, some time I called my phone and only heard my voice message. After intensive search on the internet with some suggestions such as set Network mode to GSM only etc. but nothing help much. At one time, I almost wanted to return my phone to Amazon. But I gave it one more try but go to T-Mobile and tell them to transfer my number to a newer sim. T-mobile store may give you a sim for free of charge, but since I have three newer sim card that I never used before. They just transfer my number to one of my sim card in less than a minute. I reset my network mode back to GSM/WCDMA (auto mode) and my phone did not have any issues in more than two weeks now. I hope this post will help some other galaxy s3 mini user.