iPhone 4 pricing after iPhone 5 release? Still worth it? What should I know?

I have thought about it for a long time now and decided, honestly, I hate my android device and regret ever getting it. I hate the lack of simplicity and cleanliness that it presents. Plus, the audio quality on even newer ones is significantly worse than my ipod video...

I am now interested in an iPhone, but I don't have a large budget. I am thinking about getting an unlocked iPhone 4, for use with T-Mobile, with as much storage as my wallet permits. It will be my first iPhone. I use my phone for primarily music, social networking, texting, and phone calls. Occasionally, I browse the web and play some games.

How much, roughly, will the price of an iPhone 4 go down upon the release of the iPhone 5?
Will the iPhone 4, for what I use it for, still be a worthy device to use for awhile?
Also, what features won't be available for me using this device on T-Mobile?
Additionally, buying used, how do I make sure it has a clean ESN or isn't stolen?

Thank you guys,
Brendan

We have no idea how much a used iPhone 4S will cost when the iPhone 5 is finally released. Also, you can expect to pay more if it's being sold as unlocked. As far as checking whether or not the phone is a legitimate sale, that might be difficult if it was stolen and not reported. I suppose you can always ask the seller to show you his|her original sales receipt.

An iPhone used on the T-Mobile network will only operate on EDGE not 3G or 4G as the frequencies used by T-Mobile are not the same as other US carriers. That's the primary reason why T-Mobile does not offer an iPhone of their own as do almost every other major US carrier.