If i buy a pay as you go phone - such as a xperia x8 or a sony ericsson spiro can i put my own sim in it?

[John the Baptist]

i have a sim (from my old phone which broke).. now when i buy a brand new pay as you go phone will i be able to jus take the new sim out of the new phone (throw it in the bin) then put my old sim in it and it will work?

thanks