Detect Mobile devices on loading webpage and redirect to specify URLs

Detect Mobile devices on loading webpage and redirect to specify URLs?
How do I detect different mobile devices and then display specific URLs for each category? For example If iPhone/Blackberry/PDA etc.

Sophisticated mobiles with opera and other powerful browsers then open URL1. Else not that sophisticated devices like simple virgin verizon nokia etc. open URL2 that might be just few gifs and text. Im finding trouble using PHP ASP Javascript Python etc.. Because some mobiles wont read this scripts.Share This Post on Twitter Just Click Tweet Button