For a cell phone, some already have call blocking, if not, there are free apps on the web that will work for some. You can google this. If you have a smart phone, there is a free app called call control. Iphones appear to have apps also. Another one is called Mr. Number.
For text messages: forwarding any text message spam you get to the short code “7726,” which spells “spam” on most phones, to alert your network operator to the abuse. ATT won't accept 7726 But they will accept BLOCK and return a message that the web site is blocked. forward the texts to 7726 or BLOCK, depending on your phone carrier.
http://www.att.com/esupport/article.jsp?sid=KB115812
Report your callers here, not just to the DNC alone:
To reduce the number of unwanted email and texts you receive, use these tips:
Be careful about giving out your mobile phone number, email address, or any other personal information.
Read through commercial web forms. Some websites allow you to opt out of receiving email from partners – but you may have to uncheck a preselected box if you want to do so.
Check for a privacy policy when submitting your wireless phone number or email address to any website. Find out if the policy allows the company to sell your information.
Do not respond to unwanted texts or emails from questionable sources. Several mobile service providers allow you to forward unwanted texts by simply texting it to 7726 (or "SPAM") to block the sender. Check with your provider about other options.