To associate a phone number to a vehicle follow these 3 steps:
Go to the Assets page
In the Vehicles section, double-click on the vehicle for which you want to enter the phone number
Enter a phone number on the Telephone field.
Important: Choose your correct country prefix code, and add your number with NO any other special character.
Tip: Edit your proyect location so that the prefix of the country in which you are is always displayed by default. Learn how to do it here.