UNLOCKING A BLACKBERRY BOLD TO ANOTHER SERVICE?

my friend says that you can unlock a blackberry bold to any other service and she is goin to do hers to metro pcs. but i dont think you can because those phones require a sim card. so will it work or not? because if it really does then i want to do the same. my cousin just unlocked her iphone to tmobile service because att is not doing the unlimited plan anymore and her bill is like 90 bucks