900MHz has its issues (what is this, me raging on Vodafone!

)...
The nearest mast to me is still stuck on 2100MHz O2 3G (come on O2, I'm starting to turn into the O2 version of Devon) but a Vodafone mast not that far from me but still not that close, now has 900MHz 3G on O2/VF.
The issue is, my phone now sticks to this mast despite the 2G signal from the 2100MHz mast being much, much stronger. My phone now goes from no signal, to 3G, to no signal, to GPRS, to EDGE, to 3G, to no signal, and so on, and so on...
This is making my battery life suffer. Force my G4 to 2G and problem solved (except when it rapidly changes from GPRS to EDGE - one mast to another - never used to do this, I suppose it happened when the further away 900MHz mast had O2 added). I just have to remember to change my G4 back to auto when I leave the house. Quite annoying sometimes.