Currently recent calls can be added to favorites using the phone and standard UI but not the WebUI. I think this would be a nice feature to have.
This is possible today using SSH, which can be scripted.
The command is called local_directory and a sample script would do like this:
local_directory saveentry (info for Favorite #1)
See the manual for information on how the saveentry parameters should be written.
There are several freeware programs that allow you to do this unattendedly, for example the free utility PLINK.EXE which is a command line frontend for PUTTY.
Nice thats its possible but a little silly that it can't be done through the UI. Like a lot of basic tasks that could be done through the icon UI, the answer always seems to be that it can be done using SSH commands. A 5 second task turns into installing putty on a machine if I'm not in my office or trying to use my iphone with an SSH app, then looking up the proper commands, executing them and then verifying if things are working as they should.
Retrieving data ...