Which types of phones have SIM cards ?
I recall that initially the GSM phones had them,
but don't know if they have also become mainstream
for a lot more phones that are not on GSM networks ?

I friend travelled to Egypt, and said he "bought" a SIM with prepaid calls,
and loaded it onto his phone, and then used his normal SIM the rest of the
time ??
How did he do that.... did the prepay SIM get "copied" to some internal area
?

What happens when you move a SIM from phone to phone ?

Another friend just upgraded to a new BB on Sprint (I think),
and when he was at BestBuy, the clerk "pocketed" the old SIM,
until my friend caught him, and demanded the SIM be put back into the new
BB.