PC...I don't use my iPhone 24/7.
If you are using a full qwerty keyboard for posting on a website you should be typing out your messages...honestly it doesn't take that much more effort to type on an iPhone keyboard than a regular keyboard. The only reason why anyone should be abbreviating things on a keyboad is if they are using a crappy phone keyboard (non-qwerty).
Standard internet abbreviations are different (they are generally much longer than texting abbreviations and are commonly used...on the internet). It's when you try to save time by typing regular words abbreviated that it looks stupid. You show a lack of respect for your fellow posters by not typing out what you have to say. Why should I respect what you have to say if you can't be bothered to fully type out a message you are posting?