Originally Posted by llashero
It is 18.104.22.168
Would've thought that option would be on most OSs? Very odd.
The latest is 22.214.171.124, the link to it is stickied on the top of the page (PS - did you typo 126.96.36.199?). Although the OS shows as being for another carrier (TMO), you can load other carrier's OS's on your phone safely and successfully.
That said, perhaps another 8100 user running 188.8.131.52 or .101 can confirm first if they have the option to set the number of keep days before you go to the trouble of upgrading only to find it didn't add the functionality for you.
I keep dwelling on the "new 8100 owner" part of your initial post and am hesitant to outright recommend an upgrade, knowing how scary it might be to some.
Let's see if anyone using a more recent OS can confirm or deny the calendar keep days setting. I am running an 8800, handheld v184.108.40.206 which of course isn't the same phone; but the features are purportedly similar, to my understanding.