I realise you're probably stuck in contract for a bit but you could check coverage with other providers (it'll be on their respective websites) to see if they deliver a better service.
In well over half of the places I work I barely get phone reception, let alone 3G.
Over the years I have asked a few customers if I can use their wifi, no-one has said no yet.
If I'm waiting for something important I just pull up to within reception range and use the wifi.
No-one has minded me parking so far, I've told them what I was doing.
A few have even made me a brew while I'm there, even though I wasn't cleaning for them at the time.
Selected customers obviously.