I used to have this problem quite a bit right after I got my Droid2, and I contacted Verizon for assistance. They offered me a call-blocking service that is free for up to 10 numbers, but if you want to block more than 10 numbers, they charge you an extra $5/month. I thought that was ridiculous, so I did a search through the Android Market (as it was called back then) and found a free app named Mr. Number, which also has blacklist and whitelist features as well as text message blocking. I've been using it since then and this hasn't been a bother. I have to add new numbers to the blacklist once or twice a month, and every now and then I have to block a number from a text message. Mr. Number also has a feature where you can report the spam messages to a database of spam/marketing services the publisher maintains and see other users' comments. Ironically, most of the spam text messages I get are from... Verizon (trying to sell me more "services").
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