Formatting A Phone Number

i am trying to format a telephone number (returned from the database as digits, no hyphens) to include hyphens. the database field is set as char with a length of 10. when i run the following code, i get a type mismatch error.

Private Sub formatDN(strTele)

'Changes a Telephone to a recognizable format
if Len(strTele) = 10 then
strFormatted = "(" & mid(strTele,1,3) & ") " & mid(strTele,4,3) & "-" & mid(strTele,7,4)
response.write strFormatted
Else
response.write strTele
End if
End Sub

'section of code that calls the function
HTML = HTML & "" & adoRSWEBtest(0) & " (" & adoRSWEBtest(1) & ") <br>" & formatDN(adoRSWEBtest(2)) & "<br><br>"