Does it matter if you change the SIM on an iPhone?

If i got an iPhone (4s), would it matter if (say it was on orange) I changed it to a t-mobile SIM card?

Yes. The phone is locked to Orange. Would not work on other carriers unless it was unlocked.

Yes the phone is locked to only work on orange however you can contact orange to make sim free to allw it to ise aby sime card for a small fee no more than £20