international version s3 data problem- edge signal HELP!!

[sam0621]

im using international version samsung galaxy s3 on simple mobile 4G plan, but my data signal is always edge. Before i used simple mobile $40 plan, and the signal was also edge. but my friend is using $40 plan, he gets H+ signal. also we were living together. for his phone, it is always H+, for my phone, always E... we have same setting for mobile networks. and he uses samsung nexus, i use S3. so i have really no idea what happened on my phone. so could you guys help me please~~