Verizon and AT&T are already engaged in a massive PR battle over whose wireless network is superior. Now, Sprint is jumping into the mix, unveiling a new ad which which is critical of the slow speeds on AT&T's network. The new ad touts the recently released Overdrive device, a wireless router which offers Internet access via the Clearwire WiMax network at 4 Mbps to 6 Mbps. Take a look.

Fierce Wireless reports that the ad comes just before the release of the new WiMax-enabled phone, the HTC Supersonic. The Wall Street Journal recently reported that the phone is the latest bet by Sprint to win back customers from its two larger rivals.

The Overdrive is built by Sierra Wireless. And the device reminded me of Junxion, the Bellevue startup whose assets Sierra Wireless gobbled up 19 months ago. It was unclear whether the Junxion box -- a wireless router which allowed several Internet users to share the same Wi-Fi connection -- makes up the technology behind the Overdrive.

I've got a call into Sierra Wireless to find out, and will update when I get details.

Sprint CEO Dan Hesse, who has his own connections to Seattle as the former CEO of TeraBeam and AT&T Wireless, seemed pretty bullish about the Overdrive device when it launched back in January.

“The fact that it connects up to five Wi-Fi-enabled devices is especially meaningful because at 4G speeds, customers can download and upload more data - gigabytes, not megabytes - in a matter of seconds," said Hesse. "The Overdrive on the 4G network is made for the multitude of bandwidth-hungry applications customers want to access wirelessly, like video streaming. 4G beats 3G for speed and for value.”