I was previously using e-mail to validate account registration. How do I change to use the SMS after installing the SMS plug in? Also, is there a way I can make the e-mail address optional at registration since most of my target population use sms and not email? Finally can I try the plugin using just the "demo" as sms gateway or do I need to have a gateway already before I can use the sms plugin.

@Cephas
If you enable in settings to send validation SMS, email along with SMS will be sent.
"Demo" gateway is one, that does nothing, but accept any code during verification.

ok. thank you