Trillian Basic: "It is completely free with no nag screens or built-in ads", it says on the box. Turns out that after prolonged usage, you start getting a nag screen about donating money to the project.
To remove the Trillian nag screen, you have to locate your trillian.ini file and reset the time that you have been using Trillian.
The file is normally located in "C:\Program Files\Trillian\users\default". If you chose to install Trillian in a non-default directory or if you are using multiple profiles, the file will be in a different location. Search for "trillian.ini" to find it.
The value you want to change is "Time=". Open "trillian.ini" with a text editor such as notepad and change the value to something low (the value is in seconds). 1 works like a charm.
Make sure to close Trillian before modifying the ini file and make a back-up just in case you mess something up (ctrl-c, ctrl-v).
The other way to remove the Trillian nag screen is to purchase Trillian Pro.