First - The answer is yes. Very easy to do.
Second - An IP phone normally registers to a server. You cannot register an IP phone to an OBi110.
If your IP phone can make outbound calls without registration, you can point it directly to the OBi110 for outbound calls. You might have audio problems (like one way audio) that will require some tweaking of parms. At minimum in you router you will have to port forward the OBi110 SP port and RTP ports. You will have to figure out something for inbound calls. Does your IP phone support 2 servers?
You can use another service like PBXes.org or Yate server to solve all these problems.
see:
http://www.obitalk.com/forum/index.php?topic=5411.0Third- You can point the home OBi directly to the OBi110 bypassing the OBiTalk server, but you will have the same problems as the IP phone.
Edit:
Below is an example setup for an IP phone. This setup has the OBi and the IP phone on the same LAN. You would route incoming calls to your home's public IP address and do some port forwarding in your router. Outbound calls routed to the work's public address.
http://www.obitalk.com/forum/index.php?topic=6865.0