Great topic! I've done it twice, once sort of casually and once seriously. In the second, which lasted about six months, the key was free night and weekend minutes. We'd talk for at least an hour a night. He was in Illinois and I was in D.C., so not much of a time difference. We didn't have much spare cash or vacation time, so our visits were not frequent -- a weekend every month or so. (This was before I knew about FT, of course, or I'm sure I would have been flying out to see him a lot more often!) Things ended for a variety of reasons, but a big one was that I realized he was never going to leave his small town, and I certainly wasn't about to move there.
I think you need to have some sort of long-term plan if things get serious; someone eventually needs to move, there's just no way around it (no matter how attractive the prospect of racking up millions of miles for your visits). And you have to remember that the distance tends to postpone the ordinary, everyday problems of being in each other's presence that would normally be tackled much earlier on in a face-to-face relationship. It may be easy to reach emotional intimacy when all you can really do is talk, but you're not learning how to live with each other.
Just my two cents -- I realize everybody's situation is different depending on age, temperment, where they are in life, etc.
