I agree with the others: ALWAYS hardware reset. I also use numeric result codes, but I added code after the first AT<CR> to allow an 'OK' response as well as the equivalent '0' response.

It is also important to clear your receive buffer before you begin (after the hardware reset). I usually add extra delay after reset, ATZ, ATH, etc. commands, as it seems to make it more bullet-proof.

Good luck!

-Tom