Thank you for posting with us. Yes, you can block specific numbers using your Sprint.com account. At the top of the page, mouse over 'My Sprint' and choose 'My Preferences'. Underneath the 'Limits and Permissions' header in 'All About My Account' box you will find the link for 'block voice'. If you have more than one phone on your account, click on your device and it will open up the section where you can type in the number you want to block from calling you.
Here's a more detailed blog if you need additional information.
Let me know if you have any additional questions.
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