does the Nexus 5 have a native feature to block calls and text w/o having to buy a 3rd party app just like iphone iOS7 now has such feature to block unwanted calls or text. The brief moment that I had my Nexus 5, I spent a lot of time searching for the native feature and I didn't find it, had to download a 3rd party app instead.
Actually, yes, the Nexus 5 does have native call blocking...or rather, automatically sending calls to Voicemail.
If you combine this feature with blocking the number within Google Voice, you can completely block a number.
If you're interested, this is what I did. I created a new group within my People app and named it "Blocked Numbers." Now whenever a number calls me that I don't know or want to black list, I save that number as a contact and add it to my Blocked Numbers group. Now go into that group and select the number you want to block (do this for each number), when the contact card comes up, tap the menu button and check the box for "All calls to voicemail." This specific number will never ring through your phone again, and instead will be sent directly to voicemail.
Now, if you want this number to skip your voicemail as well and you're a Google Voice user, do the following. Log into Google Voice from your web browser and go to your inbox. Find the message/number that you previously blacklisted above and click "more" (bottom of your message, next to Call and Text) and then select "Block caller." Once this is done, the number will never ring through your phone and will never reach your voicemail inbox. Enjoy.