Collectors can contact you by phone between 8 a.m. and 9 p.m., unless you tell them that they are permitted to contact you outside those hours. For example, some people may work shifts that would make it inconvenient to receive calls during those hours. 

If you are receiving collection calls, it is important to document the calls by noting the date, time of day, name of caller and collection agency, the caller ID, and details of the phone conversation or phone message.

Cary Flitter comments on collection calls: Philadelphia Magazine:  Don't Pick Up the Phone