Best way to process through a Phone number with textbox Fields in C#

I want to move through 3 textboxes to where when the user types 3 numbers for the area code, it will go to the next textbox automatically. After the 2nd textbox is complete, then it will go to the final textbox for the final 4 digits of a phone number. What is the best way to do this in C#?

Code:

<asp:TextBox ID="txtAreaCode" MaxLength="3" Width="30px" runat="server"></asp:TextBox>&nbsp;<asp:TextBox ID="txtPhoneSuffixOne" MaxLength="3" Width="30px" runat="server"></asp:TextBox>&nbsp;<asp:TextBox ID="txtPhoneSuffixTwo" MaxLength="4" Width="40px" runat="server"></asp:TextBox>&nbsp;