This could explain it: http://www.t-mobile.com/offer/free-i...uncarrier.html

Essentially tmobile has a partnership with gogo where you can text from your phone using your cell phone number and not some third party app such as whatsapp.

If the plane was at cruise altitude it wouldn't be possible to get a regular cell signal. As others have noted T-Mobile now has a partnership with Gogo. Probably just using iMessage or some other third party app that looks like texting.

You should be able to receive a cell signal until you reach around 4,000 feet AGL (above ground level). Nothing really scientific to back this up other than what I find when I go flying in my Cessna.

Guys, thanks to all!
My bad :) it's really possible to turn on wi-fi :)

If you're using the inflight Internet, your "location" is static, it doesn't change during the flight.

It is deeper than that. Tmobile enables cellular service over wifi, whereas other carriers don't. For example, you can use wifi to make a call on some Tmobile devices. You cannot do that on any other carrier.

Right. I know about the UMA technology. However, it was blocked on gogo prior to this deal. Trust me, I tried it with my UMA or as they call it now wifi calling phones. I've been using the tmobile wifi calling feature overseas for at least 7-8 years. It worked best on the samsung flip phone that did the handoff well. The new ones didn't do handoff but I read the iphone 6 handoff works well so I can't wait to try that. Apologies for the tangent. Of course this is kinda moot since you can couple the tmobile international free data with vonage to make US landline calls free of charge.

You can't do it on other carrier's devices without specific apps such as Skype or Google Voice.