pls help me those good in vb.net

i using vb.net doing project and i'm a newbie in it.i got some doubts and problems faced when i doing the project.
my project is by using vb.net design a phone that can call and sms.i wan to clear the number like the normal hp do but when i type this
Dim i As Short
For i = 0 To number.Length - 1
number = number.Substring(0, number.Length - 1)
kaopei.TextAlign = HorizontalAlignment.Right
kaopei.Text = vbCrLf & vbCrLf & number
Next i
all the numbers i type are gone instead of deleting one by one

thanks i need help badly