I mostly ignore profiles that ask for contact through whatsapp, as I don't use it and don't intend to start.
If I was keen, and the profile didn't explicitly say whatsapp only, I'd probably text and do what wound Ruth up, sayI know you prefer whattsapp but it's not an option for me. I wouldn't particularly expect a response though.
As everyone else has said, whatever the SP has stated as a preferred contact method. If it's not stated and a number is listed I would normally text first, call if it was short notice. For advance bookings email works great. It really all just depends on the situation.