Child Support and Joint Custody?

A friend of mine recently broke up with his girlfriend and they have a 3 year old son together. Currently, she has sole custody of the child and he pays child support to her, as well as pays for his medical through his employer. They split time with the child 50/50. She currently lives with her parents, has no job, and has no license (and doesn't plan on getting either from what I am told). Apparently she is living off of the child's support checks and WIC, while her parents pay for the child's needs while he is with her. I had recommended that he file for joint custody with the courts as, by definition, that is pretty much the case now. The question that I had is whether or not he would still have to pay child support should he be awarded joint custody?