The number belongs to One Call Care Management and is a company that specializes in workmen's compensation care throughout the US. Basically, a company's workman's comp carrier sub-contracts claims out to organize employee medical testing when needed.
CONFIRMED LEGITIMATE number for One Call Diagnostics. They are contracted by insurance companies nationwide to schedule medical appointments with the insurance company's approved medical providers for things such as specialty doctors (like orthopedists), imaging (like MRIs, xrays), testing, etc. I didn't recognize the number because it's different than the one I call to contact them, but a they left a legitimate voicemail requesting a callback regarding our upcoming medical appointment.