Can't you switch to Yahoo, and using 'number portability' keep your current phone number? That's what I did when I switched cellphone service providers. I told my new cellphone service provider that I wanted to keep my old number that I'd had for years, and they took care of it. However, I had to have them switch it over BEFORE I canceled out my old service! If I'd canceled first, then my old number would have gone forever.
I'd contact Yahoo tech support to find out if that's possible.
BTW, when I contacted my new cellphone service provider about the matter, THEY took care of the transfer of my number, and the cancellation of my old service. All in all it took less than 10 minutes on the phone with customer service, and less than 5 minutes after that for the changes to take affect. Super simple!