Questions in Smack's documentation

in smack’s documentation at here:

http://www.igniterealtime.org/builds/smack/docs/latest/documentation/roster.html

the “Note: typically, presence subscription is always tied to the user being on the roster, but this is not true in all cases” when talking about presence,

my question is: is there a way that I can get some users’ presence information, even though they are not in the roster?

Alex