Fortunately, as Kirk points out, it's still easy to find the IMEI number of an absent iPhone, provided you've backed it up in iTunes. All you need to do is open iTunes and go to Preferences, then select the Devices tab (second from the right). You'll see a list of device backups. Hold your cursor over one of the backups that relate to the iPhone that's lost, and you'll see various details including IMEI.
Our thanks to Kirk for pointing this out. For a longer description of the method, as well as lots more Mac-related writing, visit Kirk's website.
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