It's been a long while since I was using Linux daily, but I remember that runlevel switching to singleuser mode was at boot time from LILO (usually to fix something). I don't know what bootloader Maemo uses but it's probably similar unless things have drastically changed.
Does the phone start at all or can you not reboot it? If you changed the runlevel in a running kernel, it's likely dropped you out of runlevel 3, which is what I think is normal multiuser mode, so no X, etc., .