In the same way as oggflac allows flac playback on ogg-only devices, is there an "mp3ogg" that allows you to play ogg files on mp3-only devices?

What exactly are you asking here? . I believe you are mistaken Ogg is container format. FLAC and Vorbis files fit inside an Ogg container. MP3 could very well too, but why you would want to do that is beyond me. You don't need to encode your FLAC file in a Ogg container. The only reason you would do this is if you wanted to take advantage of Vorbis comments tags, etc. I do it sometimes.

The only thing you could do is put an MP3 inside an Ogg container, but you cannot place a Vorbis stream into an MP3 container because there is no such thing as an MP3 container. Also, what is the point? Devices that can only play Vorbis streams are not going to be able to play FLAC because they are in Ogg containers. Also - if a device can only play MP3 files it won't be able to play Vorbis files.

i was obviously way off the mark then...i was after a way to play ogg files using an mp3 decoder, lol, time to go to bed...

short answer: No.

long answer:
It looks like you are confusing container formats and codecs.

Ogg is a container format which can embed multiple codecs - audio (Vorbis, Speex, FLAC) as well as video codecs. When you refer to "ogg-only devices" I assume you mean devices that support the Vorbis audio codec. But then your statement that "oggflac allows flac playback" on these devices is not necessarily true because FLAC is a completely different codec than Vorbis. A Vorbis decoder can't handle FLAC data and vice versa. Of course there are devices that support Vorbis and FLAC but this is achieved by implementing specific decoders for both codecs.

MP3 is a different thing. It is an audio codec which also has its own file format. MP3 is not a proper container format, it's some sort of "raw data" stream. This lead to the development of things like ID3 tags and VBR headers, for instance. Meta information like that (title, artist, duration, bitrate, etc.) is normally stored in a properly defined way inside the container format. MP3 audio streams can be embedded in container formats, such as AVI, Matroska and also Ogg.

Your question about playing "ogg files on mp3-only devices" is a bit confusing. Assuming that your "ogg files" are Vorbis audio the answer is: no, a MP3 decoder can't handle that.


edit: ok, I was too slow. but my answer is the most detailed one.