I was told differently by two different AT&T agents. Since I still owe device installments they can't transfer my main number to a Nexus device unless I pay off those installments. So I have to cancel my order with Nexus because I can't pay those device installments off right now. So much for that idea. AT&T said you can switch out the SIM cards as long as you are purchasing the said devices thru AT&T. But if you bring your own device, and want to use an existing phone number, there can't be any installments due. They won't let you do that. Really makes me mad. No Nexus for me right now.