I did find the verb form of the word "text" in the Oxford Dictionaries (see the link included below), and it means just what you would expect it to mean:
send (someone) a text message: if she was going to go she would have texted us
(as noun texting) his father banned him from texting and confiscated the phone
Language is a funny thing because it changes based on new technologies as well as common usage, and it seems "texting" is now a formally accepted word.
Language is also a funny thing because we have levels of communication in which the kind of language we generally find acceptable is different for each of them. For example, the language we use to talk to friends is much less formal than we would use in an essay for class, and that language is even less formal than what we would use in what is called scholarly writing.
Obviously we all use "texting" when we speak informally, and everyone understands what we mean; we do not need the affirmation of a dictionary to use the word in that setting. Because it is now in the "official" dictionary, however, the word may also now be used in more formal writing.
[In a moment of great irony, my spell-checker just highlighted every instance of "texting" as well as "texted" in this answer]
Well, this is an ambiguous one.
Texting can of course, be used in a colloquial way - that is both valid in American and British English.
And the Oxford dictionary has officially updated its entries to include the word 'texting', along with the related 'text message'.
send (someone) a text message:if she was going to go she would have texted us (as noun texting)his father banned him from texting and confiscated the phone