Can I use a jailbroken iPhone on Virgin Mobile? I am no longer on a contract with AT&amp;T. Virgin Mobile has an awesome Beyond Talk plan for $25 (unlimited text, data, web, well I guess a max of 5.5Gb). Can I use a SIM card from a Virgin Mobile phone on my jailbroken iPhone? 

Also, is it possible to buy just a SIM card from Virgin?

TIA
No. Virgin Mobile is a part of Sprint (they used to be a Sprint MVNO). Sprint uses CDMA, not GSM, so they do not have SIM cards.

So, no iPhone on Sprint at least until Apple makes a CDMA iPhone and sells them for Sprint.