In reading this thread, I am finding a great deal of well-intentioned misinformation. I have been using Verizon Wireless BroadbandAccess with a Novatel V740 ExpressCard for the better part of a year under both OS X 10.4 and 10.5 and have never once been unexpectedly disconnected. The performance of the service itself has been excellent. I cannot say as much for Verizon's software or policies. I don't claim to know everything there is to know about this subject, but here are some important facts and corrections that may assist with more effective troubleshooting.
You absolutely *+do not need VZAccess Manager at all+* to use the BroadbandAccess service (or NationalAccess service either, for that matter) and you *+do not need an internal modem+* (or an external modem) to connect. By "modem" here, I am referring to the POTS (plain old telephone service) modem built in to some Macs (and added via USB to some others), since it has been suggested that you need such a modem in order to dial out and make a BroadbandAccess connection -- you absolutely do not.
I can state these facts unequivocally because I have had consistent and complete success connecting and staying connected with BroadbandAccess from day one without the use of VZAccess Manager (which, currently, is not installed on my system) and I do not even have an internal modem on the MacBook Pro I use to connect (and I have never used my external Apple USB modem). If you have been fiddling around with modem settings, you can stop -- they are utterly unrelated to BroadbandAccess. The broadband adapter (it is not actually a modem) is all you need to connect. The adapter is essentially a specialized cell phone that works just like other cell phones except that it only handles data communications traffic (and it requires no keypad). It has its own telephone number (just look at your Verizon Wireless bill and you'll see the number there) and it does its own dialing.
When I first signed up for BroadbandAccess service, since I knew from experience that the Mac generally "just works," I decided to try to connect without installing VZAccess Manager. After entering my account name (which is my broadband card's phone number followed by @vzw3g.com) and my password, I was able to connect immediately with no difficulties.
My only concern was that I had no way of tracking my data usage during the month and I thought that VZAccess Manager might allow me to do that. As an aside, the reason I wanted to track my usage was that, although Verizon Wireless claims that the service is unlimited, they do, in fact, forbid you from streaming video over your connection and they disingenuously claim to be able to determine whether you've been doing so by looking at how much data you have transferred. If you go over 5 GB per month, they "presume use for non-permitted uses and will terminate service." So, in legalspeak, "unlimited" means "limited" -- they've been sued for this contractual slight of hand. More, recently, Verizon has decided, instead, to charge you an overage fee of $0.49/MB for any data transfers over 5GB -- that rate is over 40 times higher per MB than the "unlimited" 5 GB included with your plan. Okay, that's a different soap box. So, hoping I could track my data usage, I went ahead and installed VZAccess Manager and used it to connect. To my chagrin, when connecting with Verizon's own software, my data transfer speed dropped dramatically (by more than half).
That was unacceptable, so I promptly uninstalled that software and went back to letting my Mac take care of the connection itself. As soon as I did that, my connection was, again, rock solid and the data transfer speed was as fast as it had been to start with. The only problem I experience now is that, when my Mac wakes up from sleep, I get a message from Internet Connect that "The selected communication device does not exist." Of course, that message is erroneous so I click "OK" to close it and I find that I am, in fact, still online without a hitch. That issue is a little annoying and I think it may be the result of VZAccess Manager leaving some vestige of itself on my system when I uninstalled it (I never received that message before I installed the software). However, that glitch is trivial in view of the vastly better performance I enjoy without Verizon's extraneous software.
So, my advice to you is to uninstall VZAccess Manager without delay and never look back. I never have. Also, watch your bill and complain if you see overage charges since you should never have to pay overages after you've signed up for unlimited service.