Mandatory keywords
From SMS Wiki
Mandatory keywords are:
opt-out: STOP, CANCEL, QUIT, END, REMOVE, OPTOUT (in Canada ARRET) When someone sends this keyword the receiving application must delete the sender's number from its database.
help: HELP, INFO (in Canada AIDE) When someone sends this keyword the receiving application must reply with description of the application, any pricing information and web site address where more information can be found.
Mandatory keywords cannot be premium.
