(half remembered, take with a grain salt) Building penetration of a signal gets worse as frequency increases - so Three UK (2100 MHz) suffers more than Vodafon

(half remembered, take with a grain salt) Building penetration of a signal gets worse as frequency increases - so Three UK (2100 MHz) suffers more than Vodafone UK (900+2100 MHz) inside large/heavy buildings. Three has LTE (4G) coverage planned at 800+1800 MHz so eventually this should improve.