I do not know if telcos in other countries also have this but here in the Philippines, there are promotions where you can use a prepaid SIM and pay a fixed amount per day/week/month which allows you to send unlimited SMS.

While this is beneficial to consumers, SMS spammers equipped with gsm modems and this promowls to send text blasts. Prepaid SIM cards are also not regulated here (no need for ids to buy one) and you can get one for about $1.