SMS position is not an application but only a plugin for Locale application.
It enable you to send SMS notification with android device.
See http://www.twofortyfouram.com/ for more information about Locale
Settings are very simple. You have to set a recipent phone number.
And you have to chose if you want to get position by network or GPS.
Position by network is fast but inacurrate. Position by GPS is accurate but can be very slow. In order to preserver battery, if GPS position is not get within 5min then network position is used.
You can prevent application to send more than one SMS by hour. Usefull if your Locale rule is fired many time...