I have had several tabs, two Android and now an iPad2. As you found the iPad does not have any USB connectivity, a major pain...but that is Apple.
Some android tabs have full sized USB
ports, some do not. Some of the full sized
ports do function in host mode, some do not. It is completely variable across the board. And then....if you wanted to use a 3G cell dongle, you would need a tab that could support that function.
You might check the new Archos G9 tabs that are coming out later this month. I hasten to note...I never actually liked Archos and do not have any connection to the company, but their new line has some very interesting specs, including a claim that they will allow the use of a 3G dongle.
ARCHOS
There are actually quite a number of new high end tabs out now from a lot of mainstream computer firms. Most are $500. You should be able to look at them in stores and then
google info online about using a 3G dongle.
Now, all this said, ever though I like tabs a lot, but they are not as useful as a full computer running Win7 (or an apple OS). A netbook that you could buy for under $300 would be more useful and would be able to use all the same drivers that a full sized notebook computer uses, since they use the Win 7 OS. You will find it easier to find and install
navigation software etc. Batt time is close to 10 hrs on most of them.
I use a combination of two laptops, an Android
phone and an iPad2 to
work online. Need all of those because I am very mobile and need to be connected full time.
Hope this helps
John