We are thinking of doing this -- sort of.
If we get TWO phones, we'll get 5K miles for each one -- so that is still 10K.
If you sign up for monthly online billing (according to the flier in the Amex bill), you do get miles for wireless payments..as I understood it. Not sure why the first poster thinks you have to get a plan for at least $59.99/month to get 'ongoing miles'.
If I've got it wrong -- feel free to enlighten me

Thanks.