Both the TRP and 3GP multimedia files are fairly common so it shouldn't be hard to find a video converter that supports both of these file types and can convert one to another.
Convert MPEG-2 HD video data to Multimedia files for wireless networks.
We have found 4 software records in our database eligible for .trp to .3gp file format conversion.
Microsoft Windows software - convert trp to 3gp on Windows
A video conversion software for MXF video
Convert from trp file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned trp to 3gp. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
A convert for TRP videos
Universal All Purpose Free Media, Audio & Video Converter Player Recorder
A multimedia converting tool for Windows