A phone call is the fastest way to get a number. Say what kind of tree it is, roughly how tall, where it stands and what worries you about it, and the crew sets a time to come and look. Estimates are free and written, and the number on them is the number on the invoice.
If a call is not convenient, send the form with your address and a line or two about the job, and you get a call back the same day. A photo of the tree from the street helps; a photo of the lean or the damage helps more.
For a tree on a house, a car or a line, call rather than write. Those jobs are dispatched first, at any hour.