can you put a t mobile sim card in an orange phone?

No You can't usually use the Sim card from Other Network in your orange Mobile normally...You need to unlock it ...Then only it accept other GSM Network Sim card.You can Unlock Orange network locked Phone using the unlock code...You can get the Free Unlock code for Old Phones at here Unlocking4free.com/free-unlocking-tools and unlock it ...It's locked Only..so you need to unlock it..After Unlock it use your T-Mobile Sim card it will accept...If you don't like to change number acll the service providers and ask the details about Mobile Number compatibility...It available means you can use the Scheme it will not change the number.