I think the best way to redirect mobile is with "Apache Mobile Filter" an open source and free project below an example:

PerlSetEnv AMFMobileHome /usr/local/AMF
PerlSetEnv AMFProductionMode true
PerlSetEnv ServerMemCached localhost:11211
PerlTransHandler +Apache2::AMFLiteDetectionFilter
RewriteEngine on
RewriteCond %{ENV:AMF_ISMOBILE} ^true*
RewriteRule ^(.*)$ http://m.foo.org [R=301,L]

you can also use AMFDetectRightFilter, AMF51DegreesFilter or AMFWURFLFilter is depend of which device repository you want to use.

For more detail: http://www.apachemobilefilter.org