this is actually your iPhone checking for email etc but because wifi goes to sleep it uses 3G hence the message.
source: the o2 website.
solution: turn off 3G when your not using it or disable push email.
- Product round-up Too 4K-ing expensive? Five full HD laptops for work and play
- Review We have a winner! Fresh Linux Mint 17.1 – hands down the best
- Vid Antarctic ice THICKER than first feared – penguin-bot boffins
- 'Regin': The 'New Stuxnet' spook-grade SOFTWARE WEAPON described
- You stupid BRICK! PCs running Avast AV can't handle Windows fixes