When someone threatens to call their lawyer, he or she could very well have a lawyer "on retainer." To have a lawyer on retainer means that the client pays a lawyer a small amount on a regular basis. In return, the lawyer performs some legal services whenever the client needs them.
Retainers are most useful for business that need constant legal work, but do not have enough money to hire a lawyer full time. Also, individuals who are likely to need a lot of legal work might want to have a lawyer on retainer.
If having a lawyer on call sounds appealing, stop and think about your legal situation first:
Finally, don't be confused by the terms "retainer" or "retainer agreement." Generally, these are not the same as having a lawyer "on retainer." When a lawyer is "retained," that means that someone has hired her, and the money paid to the attorney is known as the retainer. The agreement signed when someone hires an attorney is called the retainer agreement.
See FindLaw's articles on Meeting with an Attorney and Types of Fee Arrangements for more information.