Your phone is jailbroken isn't it?
Get backgrounder through Cydia. Create an override in backgrounder for Weather.app so when you press the home button it will close the app, not 'background' it.
My highest speed test on 3G was like 5mb or something. My bosses verizon 4 was getting around 1.5 or less. Lol!
At home on my 12mb plan with Cox I got like 9MB. Only tested it once or twice.
I remember doing the little speed test app against my two bosses droids. My 3G speed was more than...
Think about it this way, wifi hotspot will run you $20-50 per month. Paying 30 bucks in overages will equal about the same?
Or buy a Sirius radio dock or whatever and you'll be good until you get home on your wifi.
Hope I helped?