T-Mobile Unlimited plan. What will/won't work?

[TronixGT]

I have an Iphone 3G running 3.1.3 Jailbroken via redsn0w. I've installed ultrasn0w. My friend is currently with T-Mobile and has the unlimited android data plan. She wants to switch to an iPhone and I just upgraded to the iPhone 4 so I have this spare 3G.

What will I need to do when putting in her T-Mobile (USA) Sim card in to get it to work?

What will work on the iphone and what will not work?

Can you still tether using myWiFi?

I've been doing searches on here and getting nowhere as some things work for some people and not others.

As I understand.. 3G will not work? if that's the case then how will YouTube, Weather, App Store, Safari or anything data related work without 3G?

[i.Annie]

I think I answered most of your questions in another thread. But to cover the last part of your post, she can use her data. She won't get 3G speeds but she will have EDGE. So data will work fine for her.

Edit: MyWi will work fine too. The only other thing she won't have is visual voicemail in the phone app (not a big deal I assume).