I haven't noticed this posted before and I hope it helps someone.
I used to lose signal in blackspots at work and not get them back.
I had to use the airplane toggle to re-establish it.
It was worse if the phone was in my pocket as I may not notice for ages.
-I note this is not exclusive to our phone.
SOLUTION (courtsey of XDA):
1. Open the Phone dialer and type in *#*#4636#*#* (note the symbols are backwards)
2. Tap on Phone Information
3. Scroll Down and set your Preferred Network Type to GSM auto (PRL)
I'm now always on 3 or 4 bars with Vodafone (W. London)
Edited by VJJ, 28 August 2011 - 11:06 AM.