Hi weewun,
We have traveled from coast to coast and from Baja to Alaska. We had a place in Baja for 11 years where we were a distributor for DirecPC Internet Satellite Receivers. The reason for the background is to let you know we have used many, many communications systems and have bought way too many that didn't work somewhere. The bottom line, the satellite is the only way you will get reception everywhere, and only from Southern Canada down. When you head north, you will need at minimum a 4' dish with a DirecPC or similar satellite antenna. The only solution that will give you reception about anywhere you can drive, is a Global Star phone which uses digital satellite and has a painfully slow internet connection. We did use ours when absolutely required ($5.95 Min) throughout Northern Canada and Mexico. You will have to check to see if they are still in business.
I am a Senior Computer Scientist, last at the Los Alamos Think Tank, my wife a former JPL/NASA Deep Space Engineer who was on the design team and the team that supervised building and installation of the three 70 meter dishes in California, Spain and Australia that bring us those pictures of the planets from the voyager probe and others. We still do consulting and projects while on the road and still have not found the perfect system, nor stopped arguing about it.
Here is what we have found out, especially as we are now on a budget. We seldom use our computers while driving. When we do, it is generally using VOIP on our iPhones. Many, many places now have public WiFi, including most RV parks we stay at, but we do check ahead for this. Both MiFi and WiFi devices are available and it depends on what you will need to do, that should determine what system is best for you.
We have a small blog site that we put together for our friends who are interested in using technology to save money and solve problems specific to them. To keep things in one place we started the website so we don't have to keep sending the same information out. There is a very detailed article on the site about MiFi, WiFi, cell phones and 3G/4G as well as many maps and tools to see where services are available. Bear in mind that any current 3G or 4G system uses the cellular network so when you don't have cellular access, you won't have internet access, unless you use a satellite, or stop at a location that has public WiFi. There is a second article about GlobalStar satellite service if you want or need access from anywhere and it's only $39.99 per month for unlimited voice and data service (9.6 kbps) as well as other solutions. The GlobalStar article also discusses DircTV a little, and may be relevant if you travel north of the border.
The site should help you decide what is the best and the most affordable system for you. Please feel free to leave a comment or question and someone with a high-tech background (and old enough to relate to us, we're all over 50) will get back to you.
Hope this helps,
jetiii
Edit: Link moved to sig line.