That may be, but it seemed to be the charges to the corp. credit card that really made them suspicious. The cellphone seemed to just be a quick confirmation that he was still alive. Though it would seem awfully suspicious for him to abandon his cellphone without reporting it missing/stolen (even if the police tracked down the thief).

[ I'm assuming he didn't report it missing, because the article doesn't say so, and because it doesn't make sense that messages sent to unknown numbers from a stolen cellphone would mean that he's alive to investigators. ]