Do they use prepaid? Prepaid groups everything together in one flat rate. If the phones are European/European carriers and users do turn off packet data - use wifi only then it can be done.
But the only American carrier with a bring your own phone - no data is currently T Mobile. ATT has a list of phones and IMEI that they consider "smart phones" You have to get data if you wish to use ATT as a carrier. Believe me, with this damn ATT/TMO merger I have been checking and reading ATT forums.
I could use unlocked European phones with TMO and no data, but TMO would decide which "Smart phone" you had and give the appropriate data plan if you wanted data. The C6 was a 5800 with a keyboard, but TMO decided it was a TOL smartphone. You can use an unlocked phone wifi with Skype and search the web.