Best practice for BibTeX entries with paper number rather than page number

Unfortunately, there is no canonical solution here. The base BibTeX styles were written back in the late eighties when URLs and electronic journal publishing were not really a thing and journal articles and conference proceedings mostly had page numbers, so there was no need to mark up "article numbers" or "paper numbers".

Since the core styles have no provision for this, many contributed styles also don't — and if they have something, they roll their own solution; there is no standard that would encompass more styles than that of a family or of the same author.

biblatex knows the eid field, but only for @article and even there I can't promise that all styles make use of it as intended.

You will have to decide if the output looks OK on a case-by-case basis, I'm afraid.

As it so happens, you mention IEEEtran which has a paper field for @inproceedings that can be used here. That field is by no means universal and I have not seen it before, but it should hopefully give the expected output here.

The IEEEtran style provides exactly a "paper" field for this purpose, see the documentation IEEEtran_bst_HOWTO.

@InProceedings{yu2007may,
  title =    {How May E-Learning Groups Interact?},
  author =   {Yu, Chia-Ping and Kuo, Feng-Yang},
  booktitle =    {AMCIS 2007 Proceedings},
  paper =    24,
  year =     2007
}

in tmp.bib produces

\documentclass{article}

\begin{document}
\nocite{*}
\bibliographystyle{IEEEtran}
\bibliography{IEEEabrv,tmp}
\end{document}