We have had the ability to block numbers for a couple years at least:
Block or restrict voice access using My Sprint:
Sign in to My Sprint at sprint.com
Click the My Preferences tab
Under Limits and Permissions, click Block voice
Select the phone you wish to block - a green checkmark will appear indicating that phone is selected
You will see 3 choices for voice calls for the phone - click one choice:
Do not block any voice calls
Block all out-bound voice calls
Block only the following phone numbers for inbound and outbound calls
You can block calls for up to 50 phone numbers. Enter each 10 digit phone number individually or add numbers you've previously blocked (archive list numbers are saved for 90 days).
Enter the phone number you wish to block in the field and click Add number. The number will be added to the block list. To remove, select the number and click Remove.
If you do not have permissions to block voice calls, you will see a message indicating that your selection cannot be blocked.
Click the green checkmark to indicate you are finished selecting the level of restriction
Click Save to block voice access
You will see the following confirmation message: Thank you! We've saved your changes.
You will see a Blocked icon on the phone that has blocked voice services
Turn your phone off and back on for the new settings to take effect.