I have the following scenario to config & install:
UC540 w/3 SPA504 phones directly connected, 1 SPA525 phone connected via ssl vpn
Initially: AT&T will supply 4 fxo lines
In a month: service will change to AT&T FlexReach SIP trunks
Customer currently has a key-system setup; they want to continue to be able to see incoming calls on all phones
What is the best way to set this up? Do I understand correctly that key-system on the UC540 will not work with SIP trunks?