How to qualify as a new customer

We currently have bundled services with Xfinity for TV, Internet, digital landline phone and cell (Xfinity Mobile). Our cell phones are about three years old now so it's getting time to get new ones but all the best deals with Xfinity are offered to new customers.

My question is, if we decide to go with another cell service besides Xfinity, how long is the waiting period to qualify as a new customer should we decide to return to Xfinity?