What would be useful is just taking details and explaining basic of the product and service and then converting it into appointment.
Hi Chris
This is the type of service that I was thinking of...
You transfer your calls to us when you know you will be unable to answer, we answer the call "Good morning, Example Window Cleaning Services, Becci speaking, how can I help?" and deal with the enquiry with view to converting into an appointment - of which we have experience in from our commercial telesales service.
With regards to knowing your availability a Google calendar is only one option available. You guys must have a schedule for your week written down somewhere - even if you just provide us with a scanned copy of (legible) handwriting, we can then know when you will be free and can text you the details as soon as it is booked.
At the end of the day we provide you with a basic spreadsheet showing who called, when, reason for their call and the outcome.
I am not trying to over-complicate things, just trying to ascertain whether this is a potential requirement that I could provide a solution for.