I doubt it. Usually buissnesses are fine its when you get somebody's personal phone number is when they phreak out. Be careful that they don't have ANI, though. ANI as you problaly know can't be blocked.
EDIT: You really don't need to worry that much. As long as you aren't thretening phone companys usually won't do much about it. Trust me. I am sure Mike the Nextel empoyee can confirm this. Here are some tips:
1. Call from a pay phone- besides security cameras there is no real way to find out who you are
2. Use a cell phone and blocking- You can't use *69 or *57 on a cell phone. Block it, though, so caller id won't work
3. Calling card- My favorite trick. You can even sometimes spoof numbers if you call the operator before you dial your local access number. But DON'T USE THE 99 CENT STORE CALLING CARDS. THE FORWARD ANI AND CALLER ID!
4. Beige Box it- illegal but you choose who it gets traced to