US-based mobile WiMAX pioneer Sprint Nextel this week unveiled its first 3G/4G dual mode device, to be made available December 21.

The USB Modem U300, or dongle, connects to Sprint’s ‘Now’ branded mobile WiMAX network as well as the carrier’s existing 3G EV-DO network.

The dongle is manufactured by Franklin Wireless and is priced at $149.99 with a two-year subscriber agreement, after a $50 mail-in-rebate. The wireless data plans start at around $79.99 per month.

Sprint claims average downlink speeds of 2-4Mbps within the Baltimore 4G service areas, and where WiMAX has yet to launch, the dual mode device will operate on the nationwide Sprint Mobile Broadband 3G Network at average downlink speeds of 600Kbps – 1.4Mbps.

In related news, Sprint also announced plans to help developers create location based services (LBS) through a partnership with location aggregation platforms Veriplace by WaveMarket and Where by uLocate Communications. These platforms offer third party mobile, web, WAP, SMS and widget developers a consistent way to create applications that use the customer’s location information to provide customised information and services.