Block his calls, but not texts?

I want to block a number from calling, but still want to be able to receive their texts. "Do not disturb" feature doesn't work for me as it tells people I'm on another call instead of sending them to voicemail.
Are there any iPhone apps that block numbers?

Go to "Phone". Hit the circled "i" button. Scroll down and press "Block this caller". Hit block contact. If you only want to block calls, that's it, download another app.