Excel 2007 : Count no. of cells Starting with a particular value within a column

Hi everyone, I have another question...

How can I get the number of cells that start with a particular value in a column?
e.g "ST"

-------A
1 ST1253
2 SVST5
3 5012-2
4 5003-2
5 A1G03
6 A1G04
7 ST9013

The value will be "2"... but how can I do it via formula?

Thanks!
SC