I've created an Xposed module to give you a very simple and secure way to enable SMS, USSD and the native SIP dialing function on your Nexus 4, 5, 6, 7 2012 and 2013, 9, and 10. With this module you are now OTA-ready, as you don't have to revert to stock before applying an OTA, because you will not get the popular checksum error, because you don't have to flash anything (except Xposed) and thus don't modify any important file(s).
After this long time I should maybe give an update about the current status.
I red every single reply to this thread now and see there are some Nexus users having problems mainly with MMS. Well first of all I never talked about enabling MMS, but I enabled it anyway, because there isn't a difference to SMS in terms of how Google+OEMs+Providers blocked them.
That means the only reason why some of you are still not able to send and receive MMS messages is, because the provider blocks them at network level. So even though your tablet is able to send them, the providers tower doesn't even think about accepting such a message from your device, because you have a special contract.
The second problem I noticed is something I encountered myself. You will always get two pop-ups when you receive an SMS when you receive an SMS if your ROM already has an SMS receiver module like the SimpleMessageReceiver.apk that is installed by default in Googles Stock Android.
To solve that you have two options: Freeze the app in the app storage list or remove it completely. I recommend to freeze it, because a nonexistent file (after you removed it) would break incremental OTA updates.
I dropped the support for the flashable ZIP files, because they are just so uncomfortable, not cross ROM compatible, break updates, can lead to very ugly boot-loops on SOME devices without any reason. In fact, even if you copy an original framework apk from one stock Nexus 7 to another, you might even get problems there. Even though those files should be exactly the same, because the built number and md5 is the same. Very very strange and I don't have the time to investigate this.
In case you really - for whatever reason possible - don't want to install Xposed and this module, and still use the flashable ZIPs, @GuyAdams still continues to support them here. But it seems like this is for the SMS function only. You decide.
The Xposed module SHOULD work on ANY Android version, with ANY installed ROM on ANY device that is missing one of the above mentioned features. If it does not re-activate those functions on a device, you can still post it here, but Nexus devices will have priority.
If there is an important question for me you can mention me "@makuser". I currently don't have that much time, but I see @teddy0209 is already helping out a lot. Thank you very much for that! I would look out for a direct mention of my name in case anything else is unclear.
If you have any other questions, feel free to ask them
How to get it
If you don't know the Xposed Framework click here to read about it in the Xposed Module XDA-thread.
You will find the Xposed module in the Google Play Store and in the Xposed repo.
Watch it in action