Performance statistics are read from simple registry keys. Windows 98 - came with DUN 1.3, see comments above. Windows NT4 SP0 - had the same RAS functionality as Windows 95, but not supported by TMagRas. Performance statistics do not include the modem connection speed, which must be obtained from TAPI using TMagTapi. Can not delete a sub entry, only a whole connection entry.
All entries are usually in the same system wide phonebook file.
Note the RAS APIs can not access all the parameters set-up in the Windows property pages. Windows 2000 - finally added new RAS statistics functions which include the modem connection speed. Also added a lot of new security stuff for phonebook entries. There are multiple phonebook files, one for 'all users' and one for each defined user. Enumerating phonebook entries returns the location of each entry, and this should be used when editing the entry so it's saved in the correct file.