I use Twitterrific on the iPhone <i>and</i> SMS. I like SMS's because they're pushed to the phone, so I know straight away when somebody tweets. I read/tweet from Twitterrific. If (when?) Twitterrific can do push notification i'll be fine with losing SMS, but until then i'll just have to check for new tweets myself. I'm from Australia, one of the countries that just lost SMS's.