There is a project on codeplex that you can use : Mobile Device Browser File
Project Description
The Mobile Browser Definition File
contains definitions for individual
mobile devices and browsers. At run
time, ASP.NET uses the information in
the request header to determine what
type of device/browser has made the
request.
This project provides a data file that
when used with ASP.NET will detect the
incoming mobile device and present you
as the web developer with a set of 67
capabilities or properties describing
the requesting device. These
capabilities range from screen size to
cookie support and provide all the
information you need to adaptively
render content for mobile phones and
devices.
What is the Mobile Device Browser Definition File?
The Mobile Device Browser Definition
File contains capability definitions
for individual mobile devices and
browsers. At run time, ASP.NET uses
this .browser file, along with the
information in the HTTP request
header, to determine what type of
device/browser has made the request
and what the capabilities of that
device are. This information is
exposed to the developer through the
Request.Browser property and allows
them to tailor the presentation of
their web page to suit the
capabilities of the target device.