I've recently starting using eclim, which provides integration between
Eclipse and Vim. Eclipse is very good at this sort of thing. With
eclim, you can use many Eclipse features – including not only function
calls but also a full call tree, code completion, and more – right in
Vim. It's actually pretty much replaced cscope for me, which has a
known bug where function calls which have the opening '(' on a
separate line from the function name (something that happens a lot in
the codebases at my work). If you go with cscope, there's actually a
plugin for Vim which uses cscope to build a call tree:
http://www.vim.org/scripts/script.php?script_id=2368