We are an ISP, not the carrier itself. So when you order internet from an ISP, there are different carriers to chose from. Local telephone company, Covad, XO, Verizon, cable, etc. We'll order the internet line from the carrier and provide you with email, web hosting, ip addresses, support etc. So you can still order a 2nd line with us but with a different carrier so if one has an outage, you have that 2nd line to back you up. And we even tell customers the 2nd line doesn't have to be with us. Go with whoever you want but if you are going to rely on it so heavily you should have that backup connection.
As far as cost goes, you just made my point. Paying more money for a 2nd line should not be a problem. If you only have one line and goes down, how much money are you generating then?