A study carried out by developmental psychologists at Coventry University has disproved the commonly held perception that using abbreviations and other text-speak has a negative effect on literacy. Children who are proficient at texting are usually good spellers. They are more phonologically aware ie can recognise sound patterns and the relationship between letters and sounds. Texting also helps children become more aware of rhyme.
Texting can benefit weaker readers and spellers who would generally shun books and the written word, as texting can give them exposure to written English, which they would not get otherwise.
The research was carried out on 63 children aged between 8 and 12. Here's the Coventry University press release.