If you already have a smart phone with internet access as part of your contract. I think you will find most tablets have bluetooth and can be tethered to a smart phone.
So when you are out and about you can access the internet on your tablet through your phone.
For example...Earlier today I was at hospital for a few hours, I took my tablet along which is wifi only. I connected it to my wifes phone using bluetooth (she has unlimited internet with her contract). This gave my tablet free internet access. You dont need to have a 3G tablet , just a smart phone and a wifi tablet.
Make sure you check your monthly data allowance with your phone provider.