There are many P25 resources available. The PTIG web site is a very good website to start. Interested parties should always review manufacturer websites as the web sites have P25 information. The PTIG web site provides a P25 Supplier Matrix that lists the many P25 companies that are part of the overall P25 Community. The P25 Supplier Matrix document has links to the P25 suppliers.
The TIA web site can provide TIA-102 Standards documents free of charge when requested by a public safety user/agency. If you aren’t a public safety user or agency, TIA provides a link to buy or search for TIA-102 Standard documents.
For a P25 introduction of the many aspects of P25 Systems, there are good resources available. The Codan Radio Communications website provides the P25 Radio Systems Training Guide. This is an in-depth, downloadable training guide that has been available for number of years with recent revisions. Tait Radio supports the Tait Radio Academy. They offer a cost-free web video courses under the title of Introduction to P25.