Is there any low bandwidth version/hack for xmb which can be viewed on mobile phones

Not a current version. There is an really old WAP version that I think I have a copy of somewhere, but it would need someone to update it.

well, a low bandwidth is not really needed these days, with smart phones and high speed mobile internet able to view any site.
But still if there is one, which removes avatars, images etc and loads plain text, it would be good

Do you mean something like:
http://www.lottos.com.au/competitions/viewthreadlite.php?tid...

It's pretty easy - just edit viewthread.php and cut out the stuff you don't want, then edit the relevant templates. I would release it for general use, but it was years ago I did this and I would need to compare it to the full version and document it. More importantly, you would probably want some options like IP address/Find/U2U or something else that I have or have not included.