Does anyone know how how to transfer your number to another similar type of old cell phone I allready have?

I live in New Jersey.I have old At%26amp;T cell phone from long time,because of conviency I love this phone but Now it has trouble with headphone jack which is not allowing me use my headphone while I am driving.I have another similar type of phone(from old cingular) now which one of my friend gave me.These both phone has no SIM card in it.I am wondering how can I transfer my number from old phone to this phone?I will really appericate it if someone would answer.|||well...you might not be able to because they are different phone carriers...but you can always goto yr local at%26amp;t place and theyll try to do it :)