I am not familiar with kde-telepathy-text-ui, but it must provide a telepathy channel handlers. When activating the message in the indicator, it tells telepathy that you wish to handle that channel. Telepathy chooses the handler to use, which in a typical ubuntu-desktop installation is empathy. I am not sure how it chooses if there are more than one installed.
I am not familiar with kde-telepathy- text-ui, but it must provide a telepathy channel handlers. When activating the message in the indicator, it tells telepathy that you wish to handle that channel. Telepathy chooses the handler to use, which in a typical ubuntu-desktop installation is empathy. I am not sure how it chooses if there are more than one installed.