Custom Function: Count number of strings in range?

I am trying to create a custom function that would allow me to select a range and return the number of cells that contain strings within that range.

Example: If I select a range of 8 Cells containing the following list, it would return the value 3
abc
123
10/25/2010
True
def
False
=A10-B10
ghi

It would return three because "abc" "def" and "ghi" are the only three strings within my selection.

I am lost with figuring out how to determine if the cell contains a string. Any ideas?

Thanks a lot! I was able to create a custom function using your help.

Public Function StringCount(myRange As Range) As Integer

StringCount = Application.WorksheetFunction.CountIf(myRange, "?*")

End Function