In Figure 1b, the microphone gain is adjusted to accommodate the actual signal level, which solves the signal-to-noise and headroom issues. The output, however, can't be completely turned off.

My girlfriend has a Palm Pre (Sprint, not the Plus model). So far she's used it with some Sony earbuds which worked well enough, but they got pretty worn out (the headphones are about four years old).

Marshall-flavored amp-in-a-box pedals have been on the market for years, but have always come from third-party brands looking to replicate the magic of its beloved tube amps and all-valve creations.