You just proved my point, you had your laptop with you - but you just wanted to show off what you could do with your mobile device. Cool. Could it have been done if an iPhone/Android was there instead of an N900? Yes. Could it have been done quicker on your laptop? Most likely. You just wanted to show off.
ffmpeg -i "[original_audio]" -ar 8000 -ac 1 -acodec pcm_s16le -f s16le "[converted_audio].sln"