Yep experienced the same and you can tell as the signal drops straight off but when you look around you see no reason thick walls, metal clading etc.
In London its a nightmare often had my phone cut off when some convoy goes past. Wasn't it belived Gordon Browns convoy drove under the plane which had
engine failure at Thiefrow? Think it more likely a rumour.
Some companies and organsations in the UK seem to use them (if large enough to not affect those outside) from personal experince. Some Embassies I have been to appear to do this.
