help with foreign sim

[m1ckeyRAT]

hello, sorry if this question has been asked and answered. i don't have time to sift through the forums...

i'm deploying overseas VERY soon, and was wondering what i need to do to be able to use my phone overseas. i plan on buying a SIM from a local store once i arrive there. do i need to do anything special to my phone to allow me to use a foreign SIM? and do i need to flash a certain ROM and or radio?

thank you all.
m1r