Like the step-up BackBeat 326 headphones, these earphones sound quite good, particularly for the money. They have a decent amount of bass and offer impressive detail and clarity. To hear the difference between the 206 and the 326, you'll have to have pretty good ears, but we did notice that the 326 earphones offered a touch more bass (it's harder to hear the differences in higher frequencies, especially as you get older). The bass isn't as tight as what you'd get from more expensive Shure or Etymotic earphones, but you can't expect everything for $30.
Songs like the Kings of Leon's "Sex on Fire" and "Be Somebody" from the band's "Only by Night" album didn't come across with the same clarity as a pair of $150 Shure SE210s, but there was decent oomph to the tracks and we felt that even these 206 earphones bested Bose's $99 TriPort In-ear headphones--both in terms of sound and fit.
In the final analysis, the BackBeat 206 earphones may not sound quite as good as the 326, but the difference is small, so if you're on a tight budget and want to save $10, the 206 might be your best bet. As for comparisons to Altec's Classic 106 earphones, we'd suggest paying the extra dough to get these guys. The 106 headphones are also decent for the money, but they sounded a little thin compared with either the 206 or the 326 models.