How much would it cost to change a phone number if you have a T-mobile service?

I'm trying to get my phone number changed and I was wondering how much would it cost to change it?How much would it cost to change a phone number if you have a T-mobile service?
it normally doesn't cost anything. and if it does, i can't imagine it being more than a few bucks.How much would it cost to change a phone number if you have a T-mobile service?
$15 dollars unless you've moved and need it updated, than theres no charge.