As JKR clearly explains, electricity and other muggle related comforts do not work in and around Hogwarts as there is “too much magic” around Hogwarts. Hence, mobile phones which need electricity (batteries) to work would obviously not work. read more
On 1 September of the same year, Molly Weasley used a telephone to call three taxis to escort the Weasley family, as well as Harry Potter and Hermione Granger, to King's Cross Station in London to board the Hogwarts Express, an action considered brave by her family. read more