Currently only name, email and custom questions can be prefilled using a call such as `Calendly.initPopupWidget`.
See https://help.calendly.com/hc/en-us/articles/223147027-Embed-options-overview?tab=advanced#7
However, in our use case the user's mobile number is also already known. Now the user has to re-enter his mobile number, reducing conversion and introducing extra work.
It would be helpful when the mobile number for text messages could be supplied programmatically too.