I haven’t really had the chance to try out the SMS functionality of ERPnext, but it seems quite useful.
However for easier deploy-ability especially for SMEs, maybe it could be made compatible with an local Android phone based SMS gateway?
There are some nice open-source apps for that, which will probably work with minimal changes to ERPnext.
See for example:
http://www.frontlinesms.com/technologies/frontlinesync-overview/