There are a couple of issues going on in this question.  It seems to me that the best way to approach it is to take each one singularly and move from there.  If we examine "heteroglossia" as the idea of dialogic thinking, one can see how the production of text messages fits within its parameters: " [Heteroglossia is] another's speech in another's language, serving to express authorial intentions but in a refracted way."  The idea of something normative can be seen how the centripetal force serves as the monoglossic base for communication, while its manipulation is part of centrifugal force.  For Bakhtin, modern modes of communication and patterns of recognition seem to exist within this dynamic of something standardized for all and accepted by all (centripetal force) being subject to refraction and manipulation (centrifugal force):

At any given moment of its evolution, language is stratified not only into linguistic dialects in the strict sense of the word... but are also ... into languages that are socio-ideological: languages of social groups, 'professional' and 'generic' languages, languages of generations and so forth... And this stratification and heteroglossia, one realized, is not only a static invariant of linguistic life, but also what insures its dynamics: stratification and heteroglossia widen and deepen as long as language is alive and developing. Alongside the centripetal forces, the centrifugal forces of language carry on their uninterrupted work; alongside verbal-ideological centralization and unification, the uninterrupted processes of decentralization and disunification go forward.

This interplay is where the production of text messages can emerge.  The centripetal force of established language and mode of communication in keeping normative patterns through technological communication has become interspersed with centrifugal modes of communication such as texting.  The production of individual text messages becomes a form of centrifugal force interplaying with its centripetal counterpart.  For example, "laugh out loud" is a centrifugal force within the centripetal communication base.  In fact, Bakhtin might suggest that even more evidence of this centrifugal element is the notion of "textspeak" or "textspelling."  "LOL" has become an accepted pattern of recognition, a centrifugal element in a centripetal element.  "C U L8r" or "BBFN" are examples of this heteroglossia or centrifugal element within a centripetal condition.  For Bakhtin, the production of text messages represents the constant interplay between centripetal and centrifugal forces with the text language itself an example of heteroglossia.  What Bakhtin would view "as the uninterrupted processes of decentralization and disunification go forward" would be representative of the production of text messages.