I'll give my <unsolicited> vote for the OBi 200. I understand the issue with buying a $35 OBiLINE adapter that may become a paperweight, but the newer, more powerful processor in the 200 vs. the 1xx series enables it to support more features and is a bit more "future proof". If the OP has a spare telephone on hand, just try out the Comcast digitial phone service standalone (plug the spare phone into it), rather than route it into the OBi. If it turns out to be a valuable service to the OP, then buy a OBiLINE and integrate it with the OBi.
Personal opinion: I am certainly no fan of the cable companies, but the one advantage that their phone service has over most commodity SIP VoIP providers, is that much more (and often all) of the call path traverses their own, managed, private IP network, which is separated from most of the quality problems caused by inconsistent network performance via the public Internet. Aside from that, I'm dismayed at their strong-arm tactics to lock in customers with a "triple play" that just makes it less likely that the customers will defect, since they're dependent on one more thing provided by the cable company.
So, a "free trial" will simply demonstrate that it's a very good phone service, for an additional cost. You decide if it's worth it to you.