I havn't heard of that, i have 02 and a motorola rocka and not seen that option anywhere, though i would only text people who have my number anyway and so cannot see the need myself
The simple answer is, just buy a spy phone.
There expensive but you won't be able to be tracked(as in by phone signal) while using it.
Not unless sombody has another piece of equipment witch is even more expensive.
Yes you can easily and you should to use https://www.experttexting.com/ portal this is very easy an cheapest bulk sms provider you should to try it! it's free access for the first time.