If your iPhone sticks to Headphone only mode (e.g. no ringing, no signals for twitter, email etc.) try to record a voice memo -> play it back -> turn on speaker.
This helped me to recover to normal mode.
Update: no, just plug your headphones in and out again, might do the trick too 🙂
I’ve been using my blackberry as phone and email device since 2 years – and will stop it now. During my 2 weeks on holiday I had completely switched the device off, and boy: this was really relaxing. I feel I have to focus more on the work I’m currently doing and not having one of my two eyes completely stuck to the red LED of the device, always checking (even during meetings) mails, answering, editing… I am convinced, that the „always on“ mentality in itself is not the problem – it’s the „always avaliable“ thing, that made myself unproductive. I ordered an iPhone two days ago: because: I want and need an email device to be „always on“ but I want to choose when and how I read and react to emails.