Yes it can. You either have to purchase an unlocked iPhone or jailbreak and unlock it yourself after you purchase it. This process does void any manufacturer warranty.
First Jail Break it and then break baseband. there are two separate softwares which does that.
Yes it does.
No, T-mobile does not have the iPhone. AT&T has it though.
T-Mobile does not have the Iphone only At&t does
There will not be an iPhone 4S for T-Mobile but you can get any iphone unlocked at unlockatt.com
The iphone4 is not coming out on t-mobile.
Yes, the iPhone 5 has been available on T-Mobile since February 2013.
If you get it unlocked it should work. One way to make sure is that if your iphone is able to use T-mobile sim you are guaranteed your phone to work in Ethiopia.
No it is not. It is for AT&T unless you "jailbreak" and "unlock" an iphone. Instructions to do this can be found on the internet.
No.
Yes, the GSM version of the iPhone is useable on the T-Mobile network, but it must first be unlocked. If you bring an At&t iPhone to a T-Mobile store, they will unlock it, and give you a proper sim card for it.
Yes
NEVER.