Wirelessly posted (8700g)
Select the options (or settings) icon. It may be in a folder. Then select about. You will see your OS version on this screen.
Did you really mean 7100g (and not 7100t). I'll defer to others. I'm not really good with different models. Is the 'g' a GSM device? If it isn't, then you will not be able to use it on tmobile. EDIT: I see the 7100g was the AT&T version of the 7100.
What you call enterprise is BES. See BES, BIS etc at blackberryfaq.com