You can use Application.Caller, but you would probably be best to pass the cell to the function.
With Application.Caller
CallerRows = .Rows.Count
CallerCols = .Columns.Count
CallerAddr = .Address
End With
See: http://www.cpearson.com/excel/WritingFunctionsInVBA.aspx
To pass the cell:
=SomeFunction(A1)
Where the code has:
SomeFunction(r)