This is a great site. I am 20 years or slightly more older than the rest of you here. Back before caller id and 'enhanced 911', etc., two of us used to do some hilarious pranks to hotels. This was in Corpus Christi, Texas. The two of us that used to do these calls worked at a combo AM/FM radio group. We had adjacent studios. We were new, so we worked weekends from about 11pm to 7am. On Sunday mornings we used to run the hour long community programs from about 3 to 6 am. We used to dial out prank calls and record them to play to friends. We quickly found that hotels were a great source of entertainment.
Like you do, we would try to find out how full the hotels were. How many rooms were on a floor. That gave us the parameter to ask for specific room numbers. We started with the "I am the night manager and your credit card had been declined, stolen, etc. I need you to pack up, bring your bags downstairs, and checkout." Back then people had a gas card and maybe a single credit card. We would tell them that the cash rate was higher, but we do not accept cash in the middle of the night. It was fun and a bit cruel. We did some of the variations you did.
Almost caught. We did this for MONTHS AND MONTHS. About the same time every week. Eventually the hotels in Corpus Christi began to compare notes. My friend actually had a slightly later start time on his tape. One time we had to put a victim on hold so he could talk on the radio. She was listening to the radio. She right then and there figured it out. I had to start talking once she made that claim, and then she was confused by voices. It was very close.
I girlfriend of mine worked at a hotel as a front desk clerk. Of course that was the one hotel we never hit. I asked her about "prank calls to hotels" months later. She told me that the police were after a group of callers, and that they seemed to have stopped about the time they got really serious. A year or two later I told her it was us.
I would not dare try that stuff anymore with all of the caller id and traced lines. Also, the fact that I am 45 changes things a bit too. Be hard to explain to my kids!