I was reading the FAQ for the iRiver SlimX series and in one question discussing supported MP3 formats. it says:

"Note : There is no standard for VBR files; therefore, iMP350 cannot guarantee to play all VBR files."

Is this an accurate statement?

I have yet to have a LAME encoded VBR file not work on the 350. Works perfectly. Even the time display is correct. It should be noted that none of my VBR files dip below 128kbs.

This is not accurate. There is a standard which is the ISO standard.

Btw there is no major problem with IRiver units and vbr.

Is there any standard for implementation of VBR in MP3???
ISO standard has only definition of VBR and no where they talks about how to implement?
or is there any site where I can get more information about VBR implementation.

Thanks in advance!
Rgds,
Satya

The iRiver MP3 players (with latest firmware installed) have no problem playing my LAME-encoded VBR MP3s. However, their otherwise-excellent hardware suffers from timing and seeking problems if those VBR MP3s contain ID3v2 tags.

There is no standard related to how to encode, not in VBR but neither in CBR. However there is a standard describing bitstream syntax and decoding.
That is all that this important.