Or mobile phone. Pronounced to rhyme with so vile. The traditional U.S. equivalents have been, in order of adoption, cellular phone, cell phone and cell. For a true telephonic Britishism, use on (instead of at) before giving your number, as in “Ring me on 555-1212.” “In other words, the kind of people who would call in — on a mobile phone, perhaps — for Tom Petty tickets.” (New York Times, February 6, 1995)/”Once readers click on their 21st article [from nytimes.com in a month], they will have the option of buying one of three digital news packages — $15 every four weeks for access to the Web site and a mobile phone app…” (New York Times, March 17, 2011) Google Ngram.
I’d have to say that the difference between mobile (UK) and mobile (US) is on the stress and the pronunciation of the second syllable. Mobile (US) rhymes with noble and has been used for a while. I personally say mobile instead of cell in most cases because I first encountered mobile phones while working for GTE Mobilnet in the 90s.
I thought a mobile was a thing they hang over a baby crib.