Dymanic mask for C# ASP.NET TextBox in Web Form

[Joe]

I want to provide a mask for a web textbox control that will opperate to
contain a phone number as follows.

Step 1. Text Box is empty:
Step 2 OnFocus the following will appear inside the text box: (___) -
(___ ____)
Step 3 underscores are replaced as user enters data : (123) -(45_ ____)
Step 4 Example of the text box filled : (123) - (456 7890)
Step 5 user deletes a character underscore reappears: (123) - (456 789_)

This all has to happen dynamically - no submit happening.
Anyone know if this is even possible?
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