mp3wrap OUTPUTNAME FILE1.mp3 FILE2.mp3 FILE3.mp3 ...
To add ID3 tags:
id3tool FILE.mp3 -t "TITLE" -a "ALBUM" -r "ARTIST" -y "YEAR" id3v2 FILE.mp3 -t "TITLE" -A "ALBUM" -a "ARTIST" -y "YEAR"
As the man page for mp3wrap states, don't mess with the comment ID3 tag, as mp3splt needs it if you want to recover the individual files.
It seems that sometimes iTunes/iPod will stop playing these joined MP3s at the end of particular tracks, for some reason.