A "line of credit" (aka "revolving debt") (ie.credit cards, home loan, car loan, boat loan, student loans, etc.) is what is reported to a credit agency and shows up when you have your credit pulled. Each loan/lien holder that you've had for several years (7-10 usually) shows up. It show how much the debt was for (or in the case of credit cards your total credit limit), how long it has been open, and then it either says "In Good Standing" "Pays as Agreed" "Closed" "Out of Payment" etc. This is also where the delinquent payment history shows up. Most places will let you get by with the occasional late payment, it happens to nearly everyone eventually. But tech. speaking once you're 30 days late, they have the right to report you. Once you hit 90 you usually fall from their good graces and they put the dreaded "Late 90+" on your credit. One of these generally doesn't hit you too bad, but you get a second and it is the kiss of death.
"Reoccurring service charges" (ie. cell phone, home phone, etc.) are NOT reported to the credit agency. However, once you become delinquent on the payments they have every right to report you.
Lastly, if you are working to buy a house, car, etc. Anything that requires a large loan, you may want to hold off for the time being. Some cell phone companies do what is called a "hard pull" (aka hard check, depending on your location in the country) on your credit. This is the same hard pull that occurs when you are applying for a home loan, car loan, etc. Hard pull/check(s) hit your FICO score (aka "credit score") for roughly 5 points. 5 points might not seem like alot, but if you're riding close to a transition area in the FICO scale, 5 points can mean an entire 1% interest difference for a car, and up to .25% for a house. Thats a big difference in the long haul.
(Yes there is a soft check ... all those loan consolidation offers, credit card offers, etc etc come from soft checks. Soft checks do not impact your credit seeing as they only check to see that HAVE credit, not that it is good/bad.)
And as a matter of opinion, I agree with the person who said if you have a 500.00 deposit, you probably shouldn't be going after a 600.00 phone. Get a regular phone, and get a small loan for something and use the 80 bucks a month to pay it off and fix your credit.