Cscope can be a great tool to browse the Android source code. Here is what I did to get it working with vim
Get cscope_maps.vim from here and place it into your ~.vim/plugin directory. (create this dir if it does not exist)
Add the following lines to your .vimrc
if $ANDROID_BUILD_TOP !=""
"This assumes you have sourced the Android build environment
cscope add $ANDROID_BUILD_TOP/cscope.out
"Or, you can point to your android source directory in $ANDROID_DIR
cscope add $ANDROID_DIR/cscope.out
Use the following shell script to create the Android cscope database. You can add/remove search paths based on relevance to you.