Please see the 8989 code below - I am not sure how you got opted in but this should help get you removed from the sms messages.
Sprint uses a few different 4-digit short codes for free messages and self-service account management. Below is a list of some of the short codes, I will try and keep this updated as new codes are added/removed for use.
1311 - Usage and Upgrade Eligibility
This short code allows you to request your upgrade eligibility and current usage information (minutes, text and data). Text UPGRADE or USAGE.
3223 - Sprint Account Alerts
This is educational info about your new device from Sprint.
7726 - Report Spam Text Messages
Sprint is conducting a trial with a new system that gives employees and customers with CDMA devices the ability to report SPAM text messages received. Forward any text messages perceived to be SPAM to shortcode 7726 (SPAM) to report it as SPAM.
8353 - Text to Landline
Used for notifications about message delivery when texting a landline phone number that does not support SMS messaging. Either a successful or an unsuccessful message will be sent to your phone depending on the outcome.
8757 - Sprint Drive First
Used for the Sprint Drive First Android Application. These messages are normally hidden and intercepted by the device behind the scenes to signal the phone to communicate with the Drive First app.
8989 - Opt Out of SMS Messages
Send a text message to this short code with the words "end all" in the message and you will get a reply that you are removed from Sprint's SMS Message List
9000 - Picture Mail
This is the short code used for picture messages on older or simpler phones that do not support full MMS.
9016 - Visual Voicemail
Used for visual voicemail notifications. These messages are normally hidden and intercepted by the device behind the scenes to signal the phone to download new voicemail messages.
9099 - Sprint Free Msg
This code is the default used by Sprint to communicate information about an account.
9230 - Text Errors
This short code is used for information messages when there is an error with a sent text message. An example: "The short code you are attempting to use has expired, and is no longer a valid short code. Msg ####"
9999 - Block Text
This code allows you to block/unblock text messaging to specific numbers. You can text HELP to get a full list of commands. LIST will give you a list of currently blocked numbers. BLOCK (then the number) or UNBLOCK will allow you to add/remove numbers from your block list.
After cancelling the Family Locator service I 'coincidentally' started recieving random text messages about other locator services. I cannot help but feel that the privacy of my application choices has been compromised, and I will be taking this into account when it is time to renew my contract with Sprint.