These days, many consumers are ditching their landlines, making a cell phone their only phone. That's fine in many circumstances, but if you're not careful, you can easily exceed your monthly allotment of minutes and rack up huge overages. T-Mobile has a better idea: Buy one of its Wi-Fi–capable cell phones, use it to make free calls from your own wireless network or any T-Mobile HotSpot, and use your cell minutes only when you're away from a router. The Samsung Katalyst is the company's latest handset to work with HotSpot@Home, and it falls right into the middle of the lineup bracketed by the Samsung t409 and the Nokia 6086 on the low end, and three BlackBerrys—the 8120, 8320, and 8820—on the high end.