Plz help: BB 7100T T-Mob replace w/ used?

The screen on my 7100 T cracked a quarter of the way across and I would like to replace the phone now...I use it all day everyday...I am 11-12 months into my 12 month contract...T-mobile wants $250 or possibly only $150 to upgrade to a 7105T (if I can still get a rebate)...but why can't I just buy a used 7100T off ebay for $50 and put in my old sim card...will T-mobile charge me or let me do that...how does that work...can i just put the card in and away I go making callls...will it have my phone number on it somehow, I know I can get my contact list and stuff...and I think I know how to program it to recieve my e-mails but ...I know nothing about how this works...and I don't want to waste my time or money if there will be some major hitch in doing it this way. What issues will I have if any...what difficulties or downside is there to doing it this way rather than buying the upgrade from T-mobile.

Thanks for your help.

Julie

I know that your sim card is what T-Mobile uses to track your account information. I sometimes switch my sim card between my blackberry and my girl's RAZR, so you should be able to do it with another blackberry. As a matter of fact, the phone I bought before by BB was a v300 off of eBay and I used it for a few months before I got my BlackBerry.

However, I heard that the 7100 had some issues so you might want to look into finding a 7105 on e-bay if you can. I have a 7105 and I think I am wearing the buttons out from being on it so much

Also, in a couple of months, T-mobile is suppose to be coming out with another BlackBerry, which is suppose to accept memory cards and do other things. If you can hold out, I'm sure when this phone comes out there will be rebate offers for it.

If anyone knows of what this new phone is suppose to offer, can you please describe or post a link. Thanks.

Whatever you decide to do I hope you have luck in finding your new phone Julie!

do it, just make sure you by the correct model.... You just wont have your MFG's warranty....

I think what you are talking about is called the MDA...they have one called the SDA also and they have it on the website now...it is about $350 or so and the MDA and SDA have a slot for memory card...A little out of my current price range. But definately interesting to me if I can attach a file from the memory card to an e-mail and sed it off...

i would imagine that you can. You can on a Treo......