Internet Connectivity

I need a lap top that I can connect to the internet while I am travelling on Amtrak or in a car. I was considering some of the cards offered by verizon (I was even considering my cell phone-if it would work) but I wonder if you have to be stationary to use them. Also, I wonder if I should get the national network or the broadband service--I am a little bit confused as to what these entail. I am wondering if these plans are worth the money and if they are in areas where I will be where they dont roam (I love how the strong signal is the gray area on the us map but roaming is a slightly off shade of gray).

I am also going to be in Dublin, Ireland; Cardiff, Wales and Hay on Wye, Wales this fall for a few weeks and was wondering if they offered similiar network cards or if there was a cheap way to access the internet via my lap top without a land line and close proximitie to wifi establishments (which is great if they are there-I am sure in Dublin--but wales is mostly country). I dont want to haul a hughes satalitte dish around with me, I just am wondering if anyone works on their lap top through cellular companies and their experiences. What works, what doesnt--who is reliable. I am a global moderator for a hot rod message board and I love the job, but I love to travel too.

Thanks