I and my wife use regular SMS, augmented by MMS for multimedia, exclusively. No iMessage or other instant messaging. iMessage wouldn't even work anyway since I'm on Android. And that is the problem. Too many partially supported and incompatible messaging standards is the Achilles' heel of non-SMS/MMS messaging.
SMS works on everyone's phone whether or not they have a data plan, and it doesn't require a smartphone or even worse, a specific brand of smartphone. Plus it's more reliable, and uses the phone number for the ID, not an email address or some other address.
As for pricing, it's irrelevant with my carrier now, since all in-market plans have unlimited SMS/MMS anyway. This is even true for the el-crappo $20 voice-only plans, and includes both domestic and international SMS/MMS.