You can switch from AT&T to Sprint if you purchase the software to unlock the phone. As this is not what Apple had in mind you will be taking your chances on not wrecking your phone, but it can be done.
It's rumored Apple may come out with iPhone 5 sometime in 2011 that won't have SIM cards. Which means you may be able to use it with other service providers such as Sprint.
no
yes
yes you do because so far only att only carries apple iphones and things like that
Yes if you buy an iphone and use geohot's black snow and get an international sprint sim
No. It is not possible to use 2 apple ID's simultaneously on apple iPhone 4.
Verizon, Sprint, and AT&T
iphone
Sprint doesn't use SIM cards...
OSS is the Apple processing unit found in iPhones, Macs, and other apple devices. Sprint doesn't carry for Apple products so it does not have an OSS version.
The best place to get downloads for a Sprint phone is to go to the Sprint website, or use the Sprint app. Failing that, you can try iTunes if you have an iPhone, or Amazon.
Yes, but keep in mind that unlocking your iPhone is illegal and can get you in a lot of trouble.