Hi mchiao,
What exactly are your goals in using the OBI110 with the Line2 service, or what features exactly are you wanting to obtain with this setup?
Line2 'looks' to me like it is primarily an App that will run on your Droid or iOS smartphone. Is this right? Call routing appears to go straight from Line2 to your App (first via Wi-Fi if available, then 3G/4G, then cellular). If Line2 offers call forwarding features, then perhaps you could route the calls to your OBI.
Again, it really is going to depend on what you are trying to accomplish with the OBI110. If you were to get a Google Voice account, then I would imagine you could easily route your calls to both the OBI and your Line2 Number.
pc44