Usually when you post a status from your smartphone it says "via mobile". But some some of my friend post status with the model of their phone. For example, "20 hours ago via Xperia™ Smartphone from Sony".
Certain phone model specific Facebook applications add this tag to your post automatically. For example, posting from an iPhone with the notification center widget adds the "via iOS" tag. This basically happens when any application is granted permission to post on your behalf. It is up to the developer of the application what the tag says. Hope this clears things up.
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