Apple Iphone 4S - delay in getting signal?

To all you technophobes out there - my daughter has gone on contract with EE and is in possession of an Apple IPhone 4S. The guy in the shop said it could from take from 10 minutes up to 24 hours for her to get a signal - she took out the contract yesterday afternoon. To date, no signal, which is proving frustrating for her - and me, quite frankly! Any suggestions, peeps?

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