Philips, AOC, Viewsonic and ASUS monitors come with their own onsite or swapout or wait-&-repair warranty and the warranty is handled directly by their local agent as stated in the monitor documentation. The prevailing standard warranty period is 36 months from the date of purchase.
The above information is based on Compucon Quality Manual QMII 05/02/07 (4)
Philips 0800 657 447
AOC 0800 426 677
Viewsonic 0800 008 822
ASUS 0800 278 788
The usual process involves supplying the Model No. and Serial No. at the back of the monitor. They may ask you to pack it in a box and will send a courier to collect it.