Today, I came across a link from John Gruber to a rather old TechCrunch article detailing the actual cost per megabyte of an AT&T text message. Coincidentally, I had recently done similar calculations to compare the cost of using SMS versus iMessages for texting. The calculations assume that you are only using your data plan for iMessages, so consider these numbers to be a “best case” type scenario. Let’s also assume you’ll be sending 160 text characters exactly in your SMSs and iMessages, for the sake of comparing apples to apples.

Let’s look at 2 current data plans:

300 MB @ $20/mo -> 314,572,800B / 160 B =1,966,080 iMessages.

A la carte SMS costs $0.20 each, meaning the equivalent in SMSs would cost you $393,216.

3 GB @ $30/mo ->3,221,225,472 B / 160 B =20,132,659 iMessages.

The equivalent in SMSs would cost you $4,026,531.80!

Thankfully, AT&T does offer an unlimited messaging plan for $20/mo, but even so, it’s no wonder AT&T’s CEO Randall Stephenson is losing sleep over iMessages.