Yes this is possible, but not with a regular voice modem.
This set-up would require:
1) Either a FXO adapter (such as the Linksys 3102) OR a Telephony Board
2) NCH's free Axon PBX software for your office computer
3) NCH's basic (free) or business edition Express Talk software for your laptop AND (optionally) USB Phone OR a compatible SIP Phone or ATA device.
It basically works like so:
The FXO adapter connects to your phone line. Axon is set-up with the FXO adapter to use it as an External phone line. (The FXO adapter converts the Analogue line to VoIP so it can be used by Axon to make/take calls over the local network or Internet). The Express Talk softphone OR other SIP hardware you are using in the remote location will then need to be configured with an Extension in Axon. After proper configuration, you will be able to use the analogue phone line at your office from any remote destination with an Internet Connection that has the appropriate ports opened on the router's Firewall.