You could use Callentric's fax to Email service.
Get a free IP Freedom account here:
http://www.callcentric.com/products/Log into your account and under Call Treatments route all incoming calls to Fax.
In your OBi110 assuming SP2 is defined as SIP:
Voice Services -> SP2 Service > X_InboundCallRoute:
{(1?8005551212):sp2(17771234567@in.callcentric.com)},{ph}
8005551212 is the CallerID you want to route to Fax.
1771234567 is your Callcentric account number.
Edit:
You need one trunk defined as SIP for this to work.
If SP1 and SP2 are defined as GV, post back and I will show you how to get around this restriction.
Disclaimer:
This setup works for me.
Don't know if it will work on a slower network.