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You need to have the Xposed Framework installed in order to make this app/module work!!!
It is not necessary to install this app on a device already having the SMS functionality. (Galaxy Nexus, Nexus 4, Nexus 5, autre non-Nexus smartphones) This mod might also work on non-Nexus tablets though with a proper radio (2G, 3G, 4G) but with disabled SMS (by the vendor/provider).
Link to Xposed-Repo: http://repo.xposed.info/module/de.makuser.nexussms
Official XDA-Thread: http://forum.xda-developers.com/showthread.php?t=2562026