If you ware worried about running a computer 24/7 and the power usage, just get something like a HP t5700 or t5720 thin client. It runs XPe so you can load on the MagicJack software. You can pick them up off e-bay for $50-$125 (depending on the model, Mem and flash capacity). The t5700 pulls something like 12 watts and the t5720 is only slightly more.