Not seen battery drain when tethering that out paces the charger.
Asus Routers support a phone used for Tethering via a USB lead, i.e. you then use the Ethernet and Wireless capabilities of the router
£87 but supports dual WAN, so you could also use an ADSL line, or use it with a FTTC later as it can use one LAN port as an Ethernet WAN interface.
How to tether http://support.asus.com/Search/KDetail.aspx?SLanguag...
A cheaper router (no ADSL modem) is the Asus RT56U
£70 again can tether via its USB port.
Can swear by the more expensive RT-N66U
as use one every day, and runs with various alternate firmwares to give you more natty features, but comes at a price of £108
Have had mobile phones charging by USB ports on the DSL-55U and RT-N66U