I take no credit for this at all, just posting it here. This is tested and confirmed by me on SwirlyMMS 1.2.6.
This crack is posted by Colmiak at Xsellize, and I am quoting Colmiak below.
The actual fulldemo.sh according to the file itself is by geniusan.
"allright so i found this a few days ago on another thread that was deleted bc of spammers. if this thread keeps up the way it is, im sure it'll be deleted too.
so the instructions were as follows:
1. Install SwirlyMMS from Cydia
2. Install DEMO license ( there should be a file /private/var/root/Library/MMSApp/activation.lic.
3. Download attached file (fulldemo.sh) and copy to /private/var/root.
4. Connect to iPhone via SSH or PUTTY and run the script with command: sh fulldemo.sh (if does not work - sh /private/var/root/fulldemo.sh).
5. You should have 3820 DEMO days now.
6. Enjoy !
so after i installed this and tested it, my original 2 week demo license has been over for a few days now, and also installed on my g/fs iphone, her original 2 weekdemo license has been up for a few days as well but both of our phones can still send and receive MMS so im hoping it will stay like that. what that file does is give you an "extended demo," it adds 3820 days to your trial.
only drawback is that you will get the "buy" splash screen everytime you use swirly. i found a work around to this! by installing the last nonworking crack, it gives you a "valid" license and you don't have to see that splash screen anymore. remember, this crack doesn't really work, but it removes the annoying splash screen from your extended demo!"