If you have a SIP phone (a proper configurable one) you didn't really need the OBi110.
ISTR a Quick Setup Sheet with the 110 but if you've already lost that:
1. Analogue phone connected to PHONE port of 110.
2. Ethernet cable between 110 and a LAN port on the router.
3. Power supply plugged in to 110 and AC mains.
Register the 110 at
obitalk.com. "Add device".
Set up SP. Click the "Next" at the bottom right of "Obitalk compatible service providers" area, accept the "I understand .." and on the next page click on Generic and input your Voipcheap details. Click submit.