Jonnie Robinson, Curator, English accents and dialects, British Library Sound Archive, writes:
As with all linguistic varieties, opinions are divided concerning the relative merits of innovative or non-standard versions over more mainstream forms. The arrival of electronic communication has seen the rapid emergence of new written forms of English - embraced wholeheartedly by some or rejected scornfully by others, as is illustrated by this group discussion of textspeak.
The spelling of English has evolved over hundreds of years - prior to the invention of the printing press in the late 1400s, written English as practised by scribes in monasteries up and down the country took into account regional differences in accent and individual scribal quirks. In other words, nobody worried at all about the concept of 'correct' spelling - written language is after all merely a way of visually representing sounds and not a natural process in the same sense as spoken language. Nonetheless mass printing necessitated some co-ordination of method and practise and thus a written standard emerged gradually and has remained relatively fixed, although we only have to read older texts to notice that the spelling of individual words does change from time to time.
Despite the existence of a notional written standard there has always been variation in written English. A business letter is written in very different English from the sort of language we use when sending a postcard to a friend, although the spelling probably doesn't differ a great deal. We all, however, use abbreviated forms or shorthand when writing shopping lists or taking notes. The recent explosion of electronic communication has enabled other forms of written English to develop that more accurately reflect the nature of the medium. An e-mail to a friend probably differs linguistically from a letter to a friend, even if the subject of the correspondence remains the same. Textspeak is yet another example. Abbreviations and acronyms, such as I 1t u 2 for I want you to help keep the number of characters in a text to a minimum and thus speed up communication. In fact exactly the same sounds are conveyed, but in a more economic way than conventional orthography.