If switching to ATT and ordering online...

To answer your question NO, your number won't be ported until you activate your phones.

BUT IMO you really should just order new lines from the ATT website WITHOUT porting anything. Then once you get your phone call customer service and port the number over. Reason being is your order might get delayed because of the port authorization which just means unnecessary wait time.

 

I ported my number from Verizon and although it seemed like it took them forever to ship my phone, it was no longer than the others that ordered around the same time. But your situation may differ. =)

From the email I got from AT&T telling me my phone had shipped:
"Please note: Your billing with AT&T begins today. You should have inbound service by the time you receive your phone. Once you have full service (inbound and outbound) with AT&T, your account with your old service provider will automatically be cancelled. Do not cancel your service with your old service provider prior to receiving full service with AT&T."