Yes. I know this from experience. That information is immediately retrieved from startup. It just takes a moment to search your carrier status.
If it's already locked on their network - yes. If it's on another carrier's network - no.
The iPhone 3GS is only available on AT&T, but newer models are available on more carriers.
Well you technically can use a SIM Card for the network of you have an unlocked iPhone, but in most cases, you will only have access to the EDGE (very weak) network for carriers that run AWS bandwidth like T-Mobile.
You don't need to be jailbroken now that the iPhone supports most carriers. The iPhone 4 is physically unable to switch from GSM to CDMA carriers anway.
Well...As of April 2011 the American iPhone is compatible with:AT&TVerizon WirelessSprintC SpirenTelos**can also use T-Mobile's slower EDGE network with a SIM Card for those who are desparate to own these quality devices.***Once again, these are only the American carriers.
In America, the two SIM-using GSM carriers are AT&T and T-Mobile. T-Mobile can only use it's EDGE network on an iPhone with a SIM Card needed.
I don't believe any carriers still sell the iPhone 3GS or older, especially considering they offer the iPhone 4 now for free (with contract).
Right now you can get the iPhone through AT&T and T-Mobile. All you do is order a sim card and you can use T-Mobile on your iPhone. WHen it will be able through other carriers some people say will be in January when the iPhone goes to Verizon, and October when it goes to Sprint.
The Work on some Different Carriers.
You can get an iPhone at the Apple store, through carriers, or online or "brick-and-mortar" retailers.
Yes and software version
you dont