using the powerbook (or windows laptop for that matter) on the road, means you probably will be connecting via dialup 56k modem. verizon offers a dialup option with its dsl plans for (i think) $10 more a month. then you just plug into any phone and dial up, just like in the old days.
there is no need to install any verizon software. all you need is the phone number, login id and password, and have the computer set up to do ppp via modem (network system preference panel).
another option are the verizion wifi hotspots. these are publically accessible 802.11b wifi (apple airport) hotspots, that let you log in with your verizon id and password. as far as i know, they are only available in new york city, but hopefully they'll add more elsewhere.
of course, there are the usual commercial wifi services found in coffeeshops, airport lounges, etc. most of the time they are not free, but sometimes they are. and as mentioned in your other thread, some hotels offer wired ethernet access. both the wifi and ethernet are substantially faster than using the modem, but not as readily available as a phone jack.