Anyone with a 305, 786, or 954 area code has seen this… in great quantity. You receive repeated SMS messages from some dickbag towing company that offers to buy junk cars, from one of a slowly rotating group of MetroPCS cell phone numbers. Well fear not, you can stop the spamming. If you are using the Sprint network, as a Sprint, Boost Mobile, or other Sprint reseller customer, when you receive one of these, send a message to 9999 with “Spam (originating number)”. The happy Sprint anti-spam robot will reply shortly.
Its commands are all documented here : http://support.sprint.com/support/article/Block_or_allow_text_messages_from_your_phone/case-cx832318-20091103-160141