Connecting teleworker to existing analog PBX

Hi

I'm new to VOIP, but I'm hoping it can help in the following situation:

Small business office with analog PBX. Existing router with VPN to teleworker.

I'd like to plug a box into one of the PBX extensions so that the teleworker is
essentially on that extension, but via VOIP. Is that viable and if so what
hardware (at each end) is required (I'm assuming any VOIP phone like the Grandstream DP710
at sipgate.co.uk would be all that's needed at the teleworker end, but what do I need
at the office end?)

Any help much appreciated.

Tom

Post deleted by billford