Well, if you have a BUTTON PROGRAMMED you can use FEATURE 57 to do a CAMP ON.
Thus, I am certain that your *57 is something the TELCO is providing.
Now, you can restrict phones from dialing ANY STAR (*) Codes, so that may be an issue here.
Check to see if your extensions are assigned to DISSALLOW LIST 7.
DISSALLOW LIST 7 Prohibits * codes.