I think most of us really don't care that much about anonymity. I mean, unless you're making repeated, harassing calls to the same person, there really isn't that much that the authorities or a phone company is going to do. Most people don't know what *57 is, and businesses generally get pranked enough that it usually takes a while for someone to do something (plus, there's the added benefit of not always getting the same employee).
For example, I work for a call center, and the only time we EVER report anything to either a phone company or to the authorities is someone who actually got away with ordering using a stolen cc (and the order went through and shipped) or when someone finds a way to defraud us another way (my favorite was when someone got our UPS acct number and requested that we ship international packages for him and bill "his" UPS account number, resulting in us eating nearly $5000 for shipping in two months). I don't think that was ever resolved, though.
When I worked at Officemax, it was the same thing. We pursued fraud, but we never reported phone calls. We didn't have caller ID, and non-managers were forbidden from using *69 or *57, but managers never used them either.
From an Open Pantry (kind of like a 7-11/Safeway), a friend and I collect called one person about a dozen times over the course of a month. When that got boring, I would either A) call the guy at work and bill it to his wife or B) call them at home and bill it to his job. We always did it from the same gas station, and would generally call around the same time, so it should have been easy to trace, but instead he just ordered (and paid) for a collect call block and third party billing block on his line. He was sort of old, though.
I'm not saying you don't need to worry about anonymity. I'm just saying that it's not that big of a deal if you actually can be traced, unless you're doing something blatantly illegal. Then, I'd recommend buying a pre-paid phone from a retail store you don't normally shop at and just pay for it and the minutes in cash. Only use it for your harassing calls and either A) destroy it (I recommend either acid or bleach) and then "drop" out out your car window on a highway or B) load it with minutes and leave it somewhere like a bar or bowling alley where it's likely to be stolen. Let someone else be around when the vultures start circling.
