I want to have ip telephony using internet between two offices.
Two offices are connected via hi-speed internet.
How do I use VOIP to connect two offices
I dependens on the type of connection that you need.
The easiest one will be a single line phone on each end, that will ring when the other end calls.
That could be done with two Cisco ATA ‘s , around $250-$300 dollars expense.
If you have a PBX on either end, and need to be able to dial any extension withting the office remotely, you need a gateway that have FXO aned FXS ports on one end.
If you need to cconnect two offices with PBX equipment on both, that will be the most complex setup, with two gateways with FXO and FXS port.