I wish there was a way to specify to which device you want to send iMessages.

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OK, let me clarify. Her MacBook is home and is ON, kid is doing homework. Wife is away in a location with spotty cell signal. I send an iMessage to her cell number. It goes to both MacBook and Cell Phone. If it reaches at least one of these devices, it shows as "delivered". I have no way to tell if it made it to her cell phone, or if Delivered means it reached the MacBook.