The Oxford English Dictionary says yes; LOL, OMG, and FYI were added to the March 2011 release of the OED Online dictionary.
For those not versed in Web slang, OMG is short for “Oh my God,” or gosh, goodness, etc., while LOL is “laugh out loud” and FYI is “for your information.” OED says these abbreviations join others like TMI (too much information) and BFF (best friends forever).
OED notes that on the Internet or on texts, “initialisms are quicker to type than the full forms, and (in the case of text messages, or Twitter, for example) they help to say more in media where there is a limit to a number of characters one may use in a single message.”
OMG and LOL, however, have been found “outside of electronic contexts,” OED said. “The intention is usually to signal an informal, gossipy mode of expression, and perhaps parody the level of unreflective enthusiasm or overstatement that can sometimes appear in online discourse, while at the same time marking oneself as an ‘insider’ au fait with the forms of expression associated with the latest technology.”
Interestingly, OED dug into the history books a bit and found that these terms had lives before the Internet was even invented. The first quotation of OMG, for example, was in a personal letter in 1917 and FYI originated in 1941, while in 1960, LOL was used as an abbreviation for “little old lady.”
Some non-techie words also made the cut, for better or worse, including: couch surfing; muffin top; la-la land; rub-a-dub; taquito; and wassup.