There's two types of bike messengers...some are transporters, some are actually in the biz...you need to be in the know, that means getting a reference to give you their number. Then you leave a message and you'll get a callback. The first time you will usually have to meet them at a place of their choosing, but after you get to know them they'll come right up to your apt if you buzz them in.

Buy-in is alot, and the product is exhorbitantly priced, but if you want the convenience, it's worth it. Also sometimes it can take a couple of days to get a callback and up to all day to get served.

As for transporters the best thing to do is just ask. Seriously. Go to bars, ask around. You know the neighborhoods.