Yes, I am doing exactly that and it works great.
As soon as you can answer calls to the incoming number, you can add it to Localphone. They will call it to verify you can get calls there, and then you will be able to select it as your outgoing CID. You can even start doing that before you port, if you can currently answer that number.
I ported my number to Anveo about a month ago with their "no porting fee if prepaying 12 months of the $2/month plan" offer. Slick as can be.