The US took a little longer to catch on / be suckered into ubiquitous SMS than the UK / Europe didn't it? Why was that?
I assume that they were a lot slower to pick up on pay as you go phones, and most people had contracts. If these contracts had cheap rates for phone calls, there wasn't the same incentive to use 'cheap' text messages.
Notice how in series 3 of the wire there is a storyline involving cheap pay as you go phones, which when they run out of credit are just binned. The police criticise the phone manufacturers, arguing that their product is making life easier for drug dealers/ terrorists.
Of course the Wire is a work of fiction, so its probably a silly point to make