Receptionist work is tricky; even if it's the only service someone offers and especially if there's only one (1) person in the company.
Unless you have someone that will pay you for say 4 hours as opposed to "per call" it's not worth it to me. Most people want you to "be available" for those 4 hours, but only want to pay you "per call"...not equitable.
And you would also need to get an agreement that some calls 'may' go to voicemail if you have more than 1 client because (for me) it's be difficult to stop and start other tasks to answer calls and since I track time, it's even more difficult to do.
That being said...Something like Google Voice
would work well though since it shows the number that was called on Caller ID as opposed to the number calling (and works on land-lines and cell phones).
Also, a lot of the standard phone companies offer a service called "DistinctiveRing" (and other names as listed here:
) that allow you to know what number was called based on the Ringer (again making it so you would only need 1 phone).