Yep yep. In "phone.rpy" you can see in the "phone_config" variable, there are a few things that may be of interest:
"preview_no_message": "Empty chat...",
"channels_title": "Messages",
"history_timestamp_prefix": "Time:",
"phone_player_name": "Me",
"group_added": "{adder} added {participant} to the group.",
"group_joined": "{participant} joined the group.",
"group_left": "{participant} left the group.",
Just change them here and it will be good to go :)