While I was waiting for him to call, he was having a good time at the bar. This one means, both of us were doing something continuous which took a duration of time. I was waiting (and waiting and waiting) and he was having a good time (and having a good time and having a good time)... So it means I felt it was a long wait, and for the whole time he was having a lot of fun, fun, fun. While I waited... he had... also ok. It shows a snapshot contrast between the two actions both happening at the same time. Just a statement of fact, not showing duration. While I waited ... he was having... also ok. It means. Here's a snapshot of what I did: I waited. But for a continual duration of time, he was having a good time. It emphasizes that what he was doing was more exciting and active. While I have waited ... he has had... (this means it happens a lot, it's a habit).

Hi, While I was waiting for him to call, he was having a good time in the bar. Although, 'while I waited for him to call, he was having a good time in the bar' is also OK.

While I waited for him to call, he was having a good time in the bar.

While => concurrent action => -ing verbs are best used in this case.

"While I was waiting for him to call up, he had a good time in the bar.", is the best option.