Cellphone for Working Online

I always bring with me my laptop/netbook wherever I go. But the problem is that this time my shoulder is already very painful due to the weight of this. I am planning to buy a cellphone that would function like a laptop where I can still continue with my work here in myLot and my other online job even if I go to other places. But I don't know if I could afford to buy it as of now. Can you suggest what brand and model do I have to choose if ever I decided to get one? Thank you for your participation.