The great iPhone migration

February 22, 2011: 5:00 AM ET

Analysts predict that at least 2 million AT&T subscribers over the next year will switch carriers now that the Verizon iPhone is available. Here's how the companies transfer a customer's phone number from one device to another.

1. An AT&T (T) customer walks into a Verizon Wireless store to switch to Verizon's iPhone -- but wants to keep his current phone number. He provides the number and personal identification.

2. Verizon (VZ) sets up the port with Neustar, a company based in Sterling, Va., that operates the central database for telephone numbers in the U.S. Neustar's job: to make sure incoming phone calls are routed to the right device.

3. Verizon sends the switching customer's data to AT&T's customer-management system, asking it to confirm his identity. (This step helps prevent fraud.) If everything checks out, the AT&T system shoots back a confirmation and prepares the number to be transferred, or "ported," to a new device. (AT&T's GSM-based phones don't work on Verizon's CDMA-based network.)

4. AT&T is notified of the pending port and sends approval to Verizon, which tells Neustar to make the switch. Within eight seconds all the carriers are notified of the switch by Neustar.

5. The customer has a new phone that operates on Verizon's network. When a friend calls him on a Sprint phone, Sprint checks its database (a copy of Neustar's) and finds information telling it to route the call on Verizon's network instead of on AT&T's.

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