A quick search around the Wonkey Wild Web for {+”palm pre” +”wired headset” +phone} returned a number of reports of users having difficulty with their handsets being “stuck” in the wired headset mode.  As would be expected there are a host of helpful folks offering potential solutions to their troubled fellow brethren.  These include, and from Palm's own knowledgebase article, plugging and unplugging the headset jack a few times, blowing compressed air into the headset jack, and cleaning the jack with a cotton swab and alcohol.

While all of these tips make sense and are certainly appreciated, the problem looks as if it's really software related.  To be more specific, Pandora software related.  Though it's not clear as to what triggers the behavior, there may be a connection between Pandora and when it's “safe” to unplug the headset.  Regardless of how the condition is encountered, the following are the steps that were taken to successfully take a Palm Pre on Verizon out of the wired headset mode.

1. 1.With the headset unplugged, launch Pandora.
   

2. 2.Once music is playing, plug the headset in.
   

3. 3.Quit Pandora and unplug the headset.
   

4. 4.Dial voicemail (or any number) to verify that the normal mode is re-established.
   

There are a couple of things to note.  First, it may be that the reason for a device to be stuck in this mode is due to something like pocket lint being caught in the headset jack.  Therefore, the methods plenty of users have suggested may be quite valid, so some links to some of them are included below.  Also, it may also be that starting Pandora with the headset unplugged is not necessary.  So, if these steps don't help at first, try some variations of them.  For example, perhaps unplug the chord before quitting Pandora.

1. •9 Simple Fixes for the Palm Pre
   

2. •Patch Request: Disable Phone Wired Headset Mode
   

3. •Pre stuck in headset mode