freebsd-dev/release/picobsd/help/ppp.hlp.en

ppp Point to Point Protocol client
 
Usage:
 
ppp [-auto | -background | -direct | -dedicated | -ddial ] [system]
 
In case of PicoBSD most probably this will be:
 
ppp -background <system_name>
 
You should run 'dialup' script to configure automatic dialing. Then
you can use
 
ppp -background dialup
 
to connect to your provider.