For months now, T-Mobile has been running trials in Seattle for a cool new service—one that would let you make calls with your cell phone on either standard GSM networks or over a Wi-Fi connection. Now comes word from the Wall Street Journal that the service could be ready as early as next month.

Dubbed HotSpot @Home, the new service is slated to work with a pair of phones: the Samsung SGH-T709 and the Nokia 6136 (or at least, those are the phones being tested in Seattle). You'll also need a broadband connection and a Wi-Fi router (T-Mobile will give you a Wi-Fi access point if you don't already have one). Once you have everything all set up, you'll be able to place calls with your phone over your home Wi-Fi connection or at national T-Mobile HotSpot locations—and thanks to a technology known as UMA, if you wander out of Wi-Fi range, your call will be seamlessly handed off to T-Mobile's regular GSM network. That's good news if, like me, you're having trouble with reception indoors; for example, my Samsung SGH-T509 on T-Mobile barely works in my Brooklyn living room, forcing me outdoors if I want to hold a clear conversation.

So, let's talk price: according to the Journal (T-Mobile is keeping mum on its plans for now), HotSpot @Home will cost an additional $20 on top of you monthly phone bill, plus $5 for additional family members. Ugh. That said, T-Mobile could sweeten the pill by not counting Wi-Fi calls against your monthly allotment of minutes—and indeed, that's how it worked in the Seattle trials, so we can only hope the carrier will stick with that plan.

Related:
How Wi-Fi Can Extend T-Mobile's Range [WSJ, via Phone Scoop]