it is my understanding that as long as its orange it will work
you really should have work just give you a different sim or switch your sim
i wouldn't cut the sim unless i was desperate.
if work gives you a basic messaging phone and you stick the sim in an iPhone with cellular data turned on, they might get mad
as far as 3g goes, it won't matter i think, as far as i know the phone will connect at 4g/lte speeds regardless of the sim. except when it comes to cricket and they slow your speed down