It will be fine. Have asked the question myself when changing provider, can't remember the answer (I'm not really that interested other than not losing my number) but my number ported over fine.I signed up with GoMo during the week and I received my sim in the post today. When I signed up I ticked the box to keep my existing mobile number but on the sim it is a different number 085 xxxxxxxxx and my number is 087 xxxxxxxxxx. Does anyone know when I insert this new sim on the 12th of next month will it be worked from my existing number? I have sent a message to GoMo about this matter but I am waiting for their answer. I do not want under any circumstances to move from my existing number.