Specifications
3GP is defined in the ETSI 3GPP technical specification. 3GP is a required file format for video and associated speech/audio media types and timed text in ETSI 3GPP technical specifications for IP Multimedia Subsystem (IMS), Multimedia Messaging Service (MMS), Multimedia Broadcast/Multicast Service (MBMS) and Transparent end-to-end Packet-switched Streaming Service (PSS).
3G2 is defined in the 3GPP2 technical specification.
Read more about this topic: 3GP And 3G2