ATA's

With a very limited knowledge on what they actually do, I purchased one of these things the other day, expecting it to be delivered tomorrow.
Apparently it will help me choose the cheapest supplier of VOIP phone calls, coupled with changing my home phone plan to the basic ($19.95 per month) I expect to save about $25 per month off my home phone bill - the box is only costing me $74 so in 3 months time I'm already in front!
Anyone else use one of these? Any tips I may need that will help me?
Apparently it will help me choose the cheapest supplier of VOIP phone calls, coupled with changing my home phone plan to the basic ($19.95 per month) I expect to save about $25 per month off my home phone bill - the box is only costing me $74 so in 3 months time I'm already in front!
Anyone else use one of these? Any tips I may need that will help me?