Here's a first attempt. I don't have an OBi202, so you will have to be "Chief Tester" on this one!
I'm going to use these values in my example:
OBi202 sp4 ip address 192.168.1.10 UserAgentPort 5063
OBi110 sp2 ip address 192.168.1.11 UserAgentPort 5071
I have given the OBi110 UserAgentPorts 5070 and 5071 to make them different from the OBi202 UserAgentPorts – it's a sensible precaution when both devices are on the same LAN subnet.
OBi202:
Service Providers -> ITSP Profile D -> SIP -> ProxyServer : 127.0.0.1
Service Providers -> ITSP Profile D -> SIP -> ProxyServerPort : 5060
Service Providers -> ITSP Profile D -> SIP -> OutboundProxy : 192.168.1.11
Service Providers -> ITSP Profile D -> SIP -> OutboundProxyPort: 5071
Service Providers -> ITSP Profile D -> SIP -> X_SpoofCallerID : checked
The following DigitMap needs to be optimised for whatever numbers are being dialled out via PSTN. This might be typical for the UK:
Service Providers > ITSP Profile D > General > DigitMap:
(999|112|101|111|0[4568]xx.|0[1237]xxxxxxxxx)
Voice Services -> SP4 Service -> Enable : (checked)
Voice Services -> SP4 Service -> AuthUserName : 1234
Voice Services -> SP4 Service -> X_RegisterEnable : (unchecked)
Voice Services -> SP4 Service -> X_ServProvProfile : D
Voice Services -> SP4 Service -> X_UserAgentPort : 5063
Voice Services -> SP4 Service -> CallerIDName : Whatever
Voice Services -> SP4 Service -> MaxSessions : 4
Voice Services -> SP4 Service -> X_InboundCallRoute:
{5678:ph,ph2}
OBi110:
Service Providers -> ITSP Profile B -> SIP -> ProxyServer : 127.0.0.1
Service Providers -> ITSP Profile B -> SIP -> ProxyServerPort : 5060
Service Providers -> ITSP Profile B -> SIP -> X_SpoofCallerID : checked
Voice Services -> SP2 Service -> Enable : (checked)
Voice Services -> SP2 Service -> AuthUserName : 5678
Voice Services -> SP2 Service -> X_RegisterEnable : (unchecked)
Voice Services -> SP2 Service -> X_ServProvProfile : B
Voice Services -> SP2 Service -> X_UserAgentPort : 5071
Voice Services -> SP2 Service -> CallerIDName : Anything
Voice Services -> SP2 Service -> MaxSessions : 4
Voice Services -> SP2 Service -> X_InboundCallRoute:
{1234>(xx.):li}
Physical Interfaces -> LINE Port -> InboundCallRoute
{sp2(1234@192.168.1.10:5063)}
If you would like the OBi110 phone to ring as well as the OBi202 phone(s) use:
{ph,sp2(1234@192.168.1.10:5063)}
Make the usual changes to the OBi110 Line Port for UK use – change CallerIDDetectMethod to FSK(V.23), reduce RingDelay to 0.
I'm not sure how the fax fits into this setup. You might not want the incoming ring to be passed through the OBi110 to the OBi202? If so use:
Physical Interfaces -> LINE Port -> InboundCallRoute
{}
There's a fair bit of copying and pasting from other setups in the above answer, so there may be a mistake or two. If so, then you can cut my commission to half the usual amount