As far as blocking text messages, the carriers won't block them because they make money on the delivery at a rate of about $1,700 USD per megabyte when it costs them nothing to actually deliver it.
A friend has T-mob and he didn't have a messaging plan but was receiving spam messages. T-mob said that he either had to live with it or get the $9.99 plan to basically pre-pay for spam.
Congress and the FTC have been talking about investigating the unreasonable cost of messaging so I would recommend that everyone contacts their congress critters and the FTC to get some action (if that's at all possible). One way to fix it is to only charge the sender for the message like they do outside of North America, but that might screw up a lot of valid messaging from businesses like receiving a PIN from your bank to log into their web site.
https://www.ftccomplaintassistant.gov/
http://www.congress.org/congressorg/home
http://www.senate.gov/general/contac...nators_cfm.cfm
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