Nothing....well mostly. 

VoIP services do not depend on where you are located geographically and the phones store the user configuration information, so it is plug and play.

The only change you'll need to make is updating your e911 location and the Billing Contact and PBX Contact information to the new address.

We recommend when moving the phones to place a sticker on the phone with the extension or name, then place it in the box, move it and plug it in at the new location.

If everything within the network remains the same, local ISP and equipment, then you should not have any issues network related.  However network conditions may vary.