It would be interesting to see an implementation of this that doesn't require an android system at all (whether physical or virtualized), or even a live SIM card or mobile phone service.

Many VoIP SIP trunking providers will pass SMS info to an asterisk system these days (such as voip.ms and its competitors), and support outgoing SMS for replies.

All you need is a $0.85/month DID, a linux system running asterisk, and some small monthly amount of paid credit for the cost of the outgoing SMS.