I need to add something else on a few fronts:
1. The infrastructure is supposed to have backup, but a tech on DSLREPORTS claims that they are not always in working order.
2. Two phones should not be an issue with any system.
3. Any VOIP service will have difficulty running at full modem type speeds especially 56K because of the modulation technique used and the frequency response of the line. Sometimes VOIP services won't get above 14.4K and sometime 9600 baud. It's also why some FAX machines have trouble working on VOIP. It's unclear what mediacom really has. They claim it's a mix. They do offer internet service, so you could look into that.