The PhoneBoy Blog

Aircell Isn’t Blocking all Forms of VoIP

22 Aug 2008

Andy made a big splash on Twitter (and throughout the blogosphere) when he announced that he had a call on an airplane thanks to Phweet. I, of course, don’t deny it happened, but I want to warn everyone that this could easily be blocked in the future.

This probably won’t make a lot of sense without knowing what Aircell and Phweet are. Aircell is American Airlines new WiFi in the sky service that recently launched. The reported restrictions on this service are that VoIP applications are disallowed. Skype, interestingly enough, can be used without using the voice calling.

Phweet is Stuart Henshall and David Beckemeyer’s latest brainchild, making it possible for two (or more) people to set up a voice call using only your twitter credentials. No phone numbers needed. One of the ways you can connect into Phweet is through a flash widget provided by TringMe, which uses standard HTTP to communicate.

And therein lies the hole. Unlike with SIP-based solutions like SightSpeed, which reportedly failed after about 10 seconds, TringMe’s widget was able to bust through whatever Aircell is doing to block VoIP calls on the planes. The reason? The traffic looks like normal web traffic.

In some sense, that’s correct. However, if you were to look at that HTTP traffic more closely, you can figure out that something doesn’t look right about that HTTP traffic. An HTTP proxy seems to thwart the TringMe widget. Forcing the traffic through a proxy–or looking for the “signature” of this TringMe widget–is all you need to be able to block thhis flash widget without impacting other widgets (e.g. YouTube, Hulu).

Of course, like porn finds its way around the filters, you can likely find ways around this blockage. That being said, voice traffic has a certain fingerprint that is hard to mask, even if you were to encrypt the traffic. I have no doubt that Aircell, if it so chooses, could make it very difficult for this traffic to get through. I wouldn’t count on this “hole” working for long.