Android: For a much better SMS/MMS experience on Android, check out GO SMS Pro. This free app has an elegant, customisable UI and a ton of SMS features including scheduling, folders organisation, sending over Wi-Fi, and more — with very little memory usage too.
GO SMS Pro greatly improves upon the stock Android messaging app with pretty much all the features you would want for texting. You can backup your text messages to SD, email or Dropbox; batch manage messages; quickly search SMS; and much more. There's also a plug-in for Facebook Chat.
One of the nicest things about GO SMS is the interface, which is highly customisable, has a night mode, and incorporates transitions via gestures. Two widgets are also available.
Best of all, it works fast and is slimmer than other SMS apps.