I join TB now as a Vodafone hater, got my company iPhone few days ago, brilliant signal everyware, except Brackley! 
Had 3G along motorway using Last.fm app with some tunes on, turn up Brackley, bam. No signal 
What makes it funny is there is a VodaF transmitter less than 1/4 mile away! 
1 xmitter at ATS (3G), 1 xmitter on the industrial estate (GSM). Nothing else nearby - 1 at Farthinghoe. The 2 in Brackley are mount in low areas of the town.... ...now I'm no expert, but even my limited RF knowledge says thats a bit friggin dense. There are more interested in serving the A43 than they are serving a town with 15000 people.
I was in town last night. I had a minimal signal sat outside the Chequered Flag, nothing in The Greyhound (but a weak one that end of the high street) and nothing in the Red Lion. Mrs TheBoy saw me walking into town around 6ish, so dropped me a text, which I received at 8. Bearing in mind I was in the centre of a town, that shows just how poor Vodafone really are for signal.
As a test, walking home, I constantly watched signal. I got up to 2 bars near the surgery down Halse Road, dropped to 1 bar long before I passed your road tunnie, then at the crossing on Halse Road by the speed ramps, no signal at all all the way home, until I got to the kiddies playground at the end of my road, where I briefly got a signal.
Vodafone claim a full, good, indoor 2g signal across the entire town, and reasonable 3g in most areas of Brackley. They are lying bastards. There is virtually no 3g anywhere (not that i care), and, at best, intermittent 2g across the town (i do care). Hopeless.
All you can do tunnie is keep reporting poor signal via their coverage checker in the hope they may do something about it. They have told me (and at last updated their misleading map about future coverage) that their are no upgrades planned in the area (as it has full 2g coverage).
The iPhone struggles in weak signal areas worse than most.
Those more cynical than me would suggest that Vodafone have purposely reduced signal in the residential areas in order to shift more of their gay stupid suresignal boxes.