Never end a first call with a promise to call back; end it with a time
The single largest recoverable loss in most immigration practices is the inquiry that got a promise instead of an appointment.
A person calling about their status has generally called two or three firms in the same hour. The one that books them is usually the one that wins, and the callback promise puts you behind whoever answered next.
Give the person taking calls the ability to place an appointment on a real calendar, including a paid consultation, without checking with anyone. A non-lawyer can gather facts and set a time as long as the script stops well short of advice, and that boundary should be written down.
When no slot is available this week, offer the next one and take the booking anyway. An appointment ten days out that gets confirmed twice beats a callback that never happens.
Track one number: what share of first calls ended with a date. It is easy to count and it moves faster than anything you can change on the website.