My iPhone 4S and iPad 2 fail to backup to iCloud through my home WiFi either manually or automatically. It is stuck in “Backing Up… Estimating time remaining…” and doesn’t progress any further forward. Somtime it says “there was a problem completing the backup. Please try again later.” I have lots of space left for backup and backups run ok on Apple Store.
Backup iOS device to iCloud depends Apple’s servers and the Internet connection speed. I use airport extreme base stations for access points and the BT router for DHCP etc. Finaly I swap my BT Homehub for an AirportExtreme router and also configure PPPoE and DHCP on that. Issues fixed.