Is an Annuncicom 100 with standard firmware able to send/receive audio using RTP protocol ?

No, not with the standard firmware, but by using the Barix Instreamer Standard firmware or with the following ABCL firmwares it can send and/or receive RTP streams :

Annuncicom Fullduplex application contained in the ABCL firmware kit (send & receive)
ABCL IP-Intercom firmware (send & receive)
ABCL STL firmware (send & receive)
ABCL Any to ALL firmware (send & receive)
ABCL SIP Client Firmware (receive only)
Paging firmwares (receive only)

Even the Exstreamer Streaming Client can be loaded on the legacy Annuncicoms (not MPI400) to receive RTP streams

The Annuncicom60/100/200/1000 are compatible with all the here mentioned firmwares and you can find these firmwares here.