My educated guess is that it is used without a hyphen when used as a verb, and with a hyphen when used as an adjective.
Dr. Smith is on call. He is the on-call physician.
Similar to follow up:
Dr. Smith will follow up with the patient when she has her follow-up visit.
The best way to contact Oncall interpreters is through the contact section of the Oncall Interpreters website. One can choose to call Oncall or to contact them through a form online.
Yes.
It is not hyphenated.
No it's not hyphenated.
Motorcycle is not hyphenated
words are only hyphenated when they have a separate meaning when separated than they do when hyphenated
It can be. Some words can be seen both hyphenated and non-hyphenated.
No, "hardworking" is not hyphenated.
Yes it should be hyphenated.
No. Well above is not hyphenated.
The word desperate hyphenated
peace of mind is not hyphenated.