What does "does not work" mean? Nothing happens? Cursor in wrong position? Cursor not in any position? In that vein, consider that character position in a string is to the left of the character. So the periods are at position 1, 2 and 3 respectively:
.800
8.00
80.0
Since Len(defaultAreaCode) is 3, your cursor position would be between the two zeros.
If you use that as the starting point for this you should be in the wrong position.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.