I've used Boost Mobile off and on over the past several years -- here's the scoop:
Boost sells
two types of phones - one uses the nationwide Nextel network (and makes use of Nextel's walkie-talkie function). Those phones have model numbers starting with the letter "i" (such as the Motorola i296) -- and yes, since they are Nextel IDEN phones, they make use of the SIM card.
The second type of phone operates on Sprint's nationwide network -- those phones do not have the letter "i" in the model number, nor do they use SIM cards (since they operate on Sprint's network, they are CDMA phones, which do not make use of SIM cards).
As for coverage, I live near a major city -- a good rule of thumb is if you know for a fact that either Nextel or Sprint (depending on which phone you want) works well in your neighborhood, the Boost Mobile phones will, as well.
It should be noted for smartphone fans that Boost now makes a no-contract Android smartphone with the Nextel walkie-talkie built-in (Motorola i1 @
Best Buy).