I have a Samsung Galaxy S3 SGH-T999, it has some T-Mobile things on it that I have disabled as they slowed down the phone or were annoying. I am considering installing a custom ROM, but for now it is an entirely "stock" OS with Samsung and T-Mobile programs from the factory. My signal levels fluctuate, but usually stays above 2 bars. In some areas in Kitchener, the signal drops entirely, even outside, and when it doesn't drop entirely it sits at around -105db, or 0 bars. It sometimes has SMS function at those low signal levels and calling ability, and loses them even around -75db, or 4 bars, so signal isn't much of a problem.
When I send texts, they sometimes send immediately, and sometimes fail multiple times. Once it said it failed, but after retrying twice I learned it sent all three times, still having failed on my end. When I receive texts, they don't come in for a while and then there's like 5 texts all with the same time stamp with the person wondering if I'm ignoring them after they ask me something.
With calling, it sometimes works flawlessly with great quality, and sometimes an outgoing call fails to get to the other phone, or an incoming call goes to voicemail and doesn't even notify me. It doesn't even show up in the logs until later.
The SMS and voicemail both seem to arrive at the same time when there is a delay problem. Also, my brother has an iPhone 5 on the same type of plan as I and has no problems at all with signal or SMS or calling. For SMS I use the stock android messaging app. For calling I use the stock phone app. Likewise for all apps relating to calls or SMS or contacts.
What could I do, other than a factory reset, that could fix this problem?