The new phones - 3G ones - have xHMLT browser with thosands of colours, and good screen resolution - though not like the PC but most pages can be viewed in full. Its the internet connection thats expensive as its slow and therefore people tend to use WAP ot xHTML over WAP - inspite of having a device that can do a lot of multimedia.
If you tend to create a separate site for WAP / low-res based devices, you can have a separate link to it like wap.yourdomain.com or whatever.
Its difficult to check for a mobile-based browser as most have their own. Opera mobile is common though. You might want to check out
Nokia Browsing Tools.
I guess the faster way out is to check if its not PC-based IE, FF, Netscape, etc - and then do an else for non PC based browsers.
Do post if you get a solution.