TP-Link TL-MR22U is a 5200mAh battery powered 3G router with dual-chain 2.4GHz wifi and more processing power than previous hornet-based TP-Link mobile 3G router series. Default device firmware: 3.17.1 Build 140123 Rel.31844n has been made for chinese market, firmware translated to english is available: TL-MR22U_V1.0_20140123_EN.rar Installing OpenWrt is quite tricky due to signed-firmware and less than required RAM, but is possible.
Forum member pepe2k made a modification of U-Boot 1.1.4 for Qualcomm Atheros SoCs based devices (the project is still being developed, so new devices and SoCs will be supported in the future). Up to date information, binary images and sources can be found on official GitHub repository.
This modification started from wr703n-uboot-with-web-failsafe project, but supports more devices, all modern web browsers, has a lot of improvements and other modifications (like U-Boot NetConsole, custom commands, overclocking possibilities etc.).