I use that (VCO) only have one phone line. I have DSL Used to have cable internet it worked then too.
Yes, but you have a feature called 3-way calling. for some phone plans there are extra charges involved, some times it comes free with a package some times you have to order it. I have VoIP with Packet8 and 3-way calling is included for free, I have noticed however that ATT charges extra fees if you want 3 way calling ability.