Audiorealism have already proved their DSP wizardry with their plug-in emulations of these instruments for your desktop, and they reckon that technoBox's 303 emulation "features the same high-quality audio engine as ABL2 which was painstakingly optimized to be able to run on mobile devices" and boasts "aliasing free oscillators and full range non-linear filters".
Here's how the synth section looks:
It's not clear if the drums are synthesised too or come from samples, but they sure sound good either way, judging by the sound clips and videos on the site.
Of course, half the fun of those old Roland boxes was down to their built-in sequencing capabilities and naturally, technoBox has its own sequencers. The drum module features "11 parts with 808 or 909 sounds (for a total of 22 sounds) with variable amount of shuffle per pattern", while there's transpose and randomisation for the synth section. You can have 24 patterns per session (12 for synth, 12 for drums), with up to 1000 bars per pattern. Oh, and there's multitouch control of the knobs - neat!
Here's the drum module:
And here it is in action:
For the full lowdown, check out the technoBox page on AudioRealism's site.