Calling someone on their phone more than twice in one day is creepy. Seven times is downright Obsessive and Psyco.

When calling a girl or boy who's number you got, but haven't spent much time with, it is good to call within a week. Longer than that and it becomes awkward, besides the fact that they might forget who you are.

After meeting someone you are interested in and has shown deffinite interest in you, it is best not to call them more than once in a six day period. Calling more than twice total without answer nor response is Highly unadvisable. Not only are you wasting your phone minutes, but you also come accross as a desperate freak. And no one can respect a desperate freak.

When in doubt of whether or not someone that you met has any true interest or is possibly a player,
-1-ask for their number instead of giving out yours. This way you are not waiting by the phone and retain power over the situation.
-2-Be sure not to call within two full days. And when you do call, make it before six thirty pm. These things solidify the idea that you deserve respect.
-3-Do not make a second call in these situations, but leave your number and leave time constraints on when the person can reach you. This is good in numerous ways. If the doubt is that the male or female is a "player", you have sent the message that you are not a "hoochie". (Or, if you are, at least you are a respectable one!) As for if the person is just shy, now they are clear on your interest in them AND you have given a time for them to call, making their job less daunting.

When calling someone for the first couple times, make sure that you remain calm, cheerful, and friendly. I recommend written notes about ideas of when and where to meet, possible things to do, and an easy subtle mention of some characteristic they will recognize you by.