Sorry, I don't understand the meaning of your sentence, but in any case the 'it' is redundant-- and incorrect-- in the second example, because 'it' presumably is the 'cell number'. 'My cell number is back' is correct, but are you talking about a mobile phone number or a prison cell number? How could either return?
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.