One thing that's very apparent with the hf2s is that a good seal is vital to achieving the best sound quality. Because these earphones favour high end clarity, if you don't have a good seal, you'll end up with pretty much no bass whatsoever, and a very harsh sound overall. Once again, I'd recommend using foam tips, and even though I doubt Etymotic will like me saying it, some Shure foams to really get the best out of these earphones.
Considering that the ER.4 microPros cost £190 when I reviewed them back in 2006, I fully expected the hf2s to come in at a similar price. Surprisingly though, the MSRP for the hf2s is £100, which probably means that you'll be able to pick them up a little cheaper than that online, once they hit the channel. You can pick up Shure's SE310s for around this price, and I'd say that they have the edge over the hf2s when it comes to sound quality. However the Shure's don't let you talk on your iPhone while it's in your pocket - unless you buy the MPA, and that's adding another £40 to the price.
The earphone upgrade market is becoming ever more crowded with quality products, but if you've just bought yourself a shiny new iPhone and don't already have a decent set, the Etymotic Reseach hf2s make a very good case for themselves.
If you're an iPhone user you won't need much convincing that the hf2s represent the perfect replacement for the awful set that comes in the box. The sound quality is a little light on bass, but impressive nonetheless, while the microphone makes taking calls a breeze, even in noisy environments. The ability to pause your music and skip tracks without taking your iPhone out of your pocket is also a bonus.
If you're major concern is sound quality, then you're probably better off looking at a set of Shure SE420s and a Shure Mobile Phone Adapter to go with it, but that's going to cost you far more. For most users though, Etymotic has produced the perfect companion for your iPhone.