iPhone 4 3G slowed down immensely all of a sudden

so i've been having issues 3g on iphone 4, i've restored backup twice, didn't change, did restore factory settings, reset network settings multiple times, went at&t , got new sim card, tried imaginable (i think). after it's still running slow. downloaded "speedtest.net" app. ran couple of tests, made friend download same app, has at&t. came 0.05mpbs - 0.11mpbs while came 1.17mpbs - 2.01mpbs. both on 3g, both on iphone 4, both on at&t, both in same building. have no idea else do, suggestions?

 

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