Help with USA internet device and I Phone

So two (probbably very basic) questions for all you IT/iPhone expert type persons
1. Mobile internet hotspot device thingy
I remember that people have mentioned a device that generates a mobile hot-spot what you can then attach your laptop (and other devices) to (and so avoiding the exhorbitant hotel charges) but I can't remember the name of the device or the company that sells it.
2. Help with iPhone
I have a new (to me) iPhone 3GS that is tied to O2 that I want to use in the USA. I understand that I need to get O2 to unlock the phone so I can use a USA sim card in it
Can any one recommend a suitable package. I will be in the US for a week (this trip). I won't be using the phone/text side very much but will want the data side - posting on FB and on here and some other apps for example. Do I really need a data package or can I get away on using free hotspots for that side of things and a cheap paygo sim for text and calls?
Thanks for the help.
1. Mobile internet hotspot device thingy
I remember that people have mentioned a device that generates a mobile hot-spot what you can then attach your laptop (and other devices) to (and so avoiding the exhorbitant hotel charges) but I can't remember the name of the device or the company that sells it.
2. Help with iPhone
I have a new (to me) iPhone 3GS that is tied to O2 that I want to use in the USA. I understand that I need to get O2 to unlock the phone so I can use a USA sim card in it
Can any one recommend a suitable package. I will be in the US for a week (this trip). I won't be using the phone/text side very much but will want the data side - posting on FB and on here and some other apps for example. Do I really need a data package or can I get away on using free hotspots for that side of things and a cheap paygo sim for text and calls?
Thanks for the help.