Calculate Earth global distances

I wrote this sp to be able to calculate the distance between two locations on the earth if the latitude and longitude is known for each.  Could be useful for GPS work or maps.

Usage:
If I know the following city locations:
Sydney         151.2 E             33.87 S
Canberra       149.15 E             35.24 S

DECLARE @RC int
DECLARE @Dist decimal(28,20)
EXEC @RC = [dbo].[sp_EarthDistance] 149.15, -35.24, 151.2, -33.87, @Dist OUTPUT
Select @RC, 'Distance from Sydney and Canberra = ', @Dist

Result (kilometers):
0           Distance between Sydney and Canberra =  242.04260703665335000000

You can change the precision or distance units yourself.