I believe that you have to give Verizon a call to unsubscribe.
Checking all the past "cancel NFL Mobile" strings, the majority of them appear to say
texting STOP to 69635 is the solution. At least it seems to be one of the solutions.
I know that now that NFL season is over, many are looking to remove the NFL Mobile Premium application. As @tikibar explained, you may find an answer within another forum post, http://bit.ly/Y80stc . This information is beneficial because it gives you a screen shot of what you will see when removing the application.
If you have any additional questions, feel free to keep us posted.
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