New version going up in next 24 hours. Addresses much of My Lucky's comments above. SMS replies are almost natural, intuitive now.
Also really excited about what I am currently calling "GASP", for "GPS At Shutdown Point": in the fraction of a second left before a (lost) phone's battery dies completely (or the phone's switched off), PhoneLeash will send out the phone's location. This has nothing to do with SMS forwarding of course, but you heard it here first.