Your understanding is spot on, but applies to a "dedicated data device with service" -- for instance, using a USB modem to provide internet connectivity to the computer it is attached to.
while that is the more popular approach to get mobile broadband service, my response isn't about that, and describes a way to provide what you had asked for in you earlier post (quoted below):
Bcam wrote:
accessing the internet when on the road periodically for relatively short periods of time without committing to a long-term high monthly fee
I don't know what carrier you currently pay $70/mo for cell/voice phone service but:
- if it is Verizon, AND
- at least one of those phones is capable of accessing verizon high speed data service, AND
- if that phone can be tethered to laptop
then you can call verizon and tell them to activate the "data feature" for that phone, which allows you to surf the internet on your computer, while it is tethered to your phone -- when and where you need to.
This does not require a separate contract to do this, its a verizon feature you can enable/disable when you need it. IF you were to have the feature enabled for an entire month, it could add as much as $60/mo to your bill.
BUT, if you only need casual/infrequent use and remember to call and disable when you are done using it, then Verizon will PRO-RATE the monthly service for the days you have that "data feature" enabled. This exactly addresses what you asked for in later post: (quoting again)
Bcam wrote:
I want to spend a few dollars for a few days or couple of weeks, pay nothing for two or three months, pay for a few days and so on.
Hope that clarifies things enough? if not, ask another specific question and i'l do my best to answer.