Difficult questions you have;
ad 1/ Generally, if Antitheft is installed and set on, any change of SIM card will lead to possible lock of the device. Sent SMS will be delivered in dependence of the vendor you did use (they are caching the undelivered SMS messages for some time and try to execute them in any possible time the device is logged in BTS); if so, antitheft will receive them and will perform the action.
ad 2/ We experienced some errors with Google Voice service and with custom SMS managers, those are fixed in last update from yesterday :-( But the antiheft is really smart on it, so generally, yes, there is a chance that SMS command will take an effect on the lost device.
ad 3/ No, lock text will only display a message for unauthorized person trying to use the device. It can not show your pattern anyhow.