So... reliability is key.
But, so is cost.
I've tried several options... SKYPE (not ready for prime time), POTS (great quality, high cost, limited flexibility for SOHO), Alternative VOIP, CELL, and VONAGE. My pick for home based reliability - Vonage.
Why?
Lots of reasons.
First, the quality has gotten VERY good. Consistently good (assuming you have great internet high speed).
Second - COST. It's predictable (25 bucks a month - ALL YOU CAN EAT). That's cheap.
Third, it's highly flexible when it comes to a SOHO. If it's down (rare)... you can configure it to ring your wireless (or any other number). If you're working in a "real" office for a day (or a month)... you can set it up to automatically forward - seamless to your callers. AND - you can even set it up using a great feature called SIMULRING™... so that it rings your VONAGE number PLUS another number (or more than one) that you define.
That's great flex... for a great price.
And that's what you need to make SOHO Great.