iPhone issues, locking up black screen etc...

the last week or so ive had issues with the phone locking up for extended periods and currently it froze up after a phone call unfroze for a second when i held the top button so that i could power it off. got it to give me the slider to power off now its has a black screen. im still able to sync it and i did that and downloaded all the stuff i hadnt yet. is this some issue that att can fix or give me a new phone or something. getting frustrating. its a first gen phone purchased in jan of 08. if they do replace will i get anohter first gen or will they make me upgrade to a 3g and if thats the case do i have to pay for it?

Have you tried doing a Restore?

Restore is the best bet, another idea is to make sure you turn of your iphone. I believe leaving your iphone on for prolonged periods of times can cause errors such as the ones you have described. Or it could be a dust build up in your phone.