Your son will probably have to contact his mobile phone provider (Orange, Vodafone, T-Mobile, O2) and ask them for the number. They may need to activate the e-mail facility on his account.
Huawei P10 review
1995-2015: How technology has changed the world in 20 years
How VR is being used to simulate space
New iPad, iPhone SE & Red iPhone 7 on sale now
Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.