While there is some variety of mobile headsets, they only come in certain styles and tend to be of low quality.  It's a little-known fact that with the right adapter, you can use a professional office headset with almost any cell phone and many cordless phones.

Why would you want to use a professional headset?  Professional headsets come in a huge number of styles, including styles that you might not find for mobile headsets, e.g. binaural (both ears), behind-the-head, over-the-ear, and in-ear.  The main benefit of a professional office headset is its comfort: they're designed to be used all day. Professional headsets tend to be high quality - light weight, well-built, with decent audio quality, and with low-cost replacement parts (e.g. ear foam).  Many people use their cell phones as their primary phones, so it makes sense to use a high-quality headset instead of a cheap mobile headset.  Any headset can potentially save you a lot of neck pain.

The Plantronics 2.5-mm adapter, part number 43038-01, costs less than $10 and lets you connect any Plantronics H-series headset to any cell phone or cordless phone with a standard 2.5-mm jack.  Nearly all new cell phones and most high-end cordless phones have these jacks (older Nokia phones had a proprietary 2.5-mm jack).  You can find 2.5-mm adapters for most old cell phones as well.  H-series headsets terminate in a Plantronics "Quick Disconnect" plug.

I use a Plantronics H101N with my Nokia cell phone. The ~32-inch cord on the headset plus the 18-inch length of the adapter cable is a comfortable length for use with a cell phone or cordless phone.  The H101N is binaural, which for me, means I can hear more clearly without the need to turn the volume up to potentially dangerous levels. The audio quality is decent - good enough for typical voice applications, though if you listen to music, a lack of high frequency response becomes apparent. The headset is extremely comfortable, even when used for long periods, thanks to its light weight, soft foam, swiveling earpieces, and adjustable headband.

I also have a Plantronics H31N. This is an in-ear model, designed to make a seal in your outer ear canal, thus blocking some background noise. The audio quality is not great - just good enough for voice. And the supposedly "noise-canceling" microphone picks up a lot of background noise and is susceptible to wind. But the in-ear ear pieces do what they're supposed to: they block a great deal of outside noise, making this headset my first choice for loud environments. Using the dual VersaTip kit, the H31 and H31N are binaural - though the passive nature of the VersaTip means that the sound in one ear is somewhat louder than in the other.

With the right adapters, the same headset can be used with other types of devices:

Other accessories:  (see the Plantronics Products + Accessories Guide PDF)
Don't forget to check eBay for good prices on headsets.