10:30am guy turns his phone on, 1:30pm he turns it off. You call between that time, he picks up tells you to come to one of three locations, you order in code from a pre-determined menu, bring exact cash to the location. He pulls up, you hop in his car or he hops in yours and you make the exchange. Very simple, very effective, and if the locations are well picked out (and they are, this particular dealer is so PRO) the chances of getting in trouble with the law are greatly decreased.
Other people you just call and then you go to their house.. or a house set up to deal (one of my dealers had 2 apartments, 1 for dealing one for sleeping/living).
The only ridiculous method I've seen (people talking about fast food drive-thru people selling drugs that is the dumbest shit I've ever heard of and, knowing a bit about how fast food restaurants are setup and run, I call bullshit. Anybody doing something like that without other employees/managers turning a blind eye would be caught within a month or two.
Anyway, I used to work at a restaurant valet parking cars. We used a parking deck next door. The deck is also a pay lot so anybody could pull up to the gate, grab a ticket and be let in. My co-worker would have his customers pull up to the gate, grab a ticket, and enter the parking deck then drive to a specific area where we valet cars. Co-worker would hop in the customer car and have them drive him to the exit gate while he put their order together and counted the money etc. At the exit gate he would hop out, swipe his card to let them out, and return to work.