As I'm going to be staying away from home next week in a Bangkok hospital. I've bought a new ZTE MF631 7.2 Mbps DL Aircard so that I can use the internet , I'll be using this device with an AIS prepaid 600 minute sim. I notice that the Aircard supports a micro SD card. Is a Micro SD card required to make the thing work or will it function happily without one. What are the benefits of using a Micro SC card with this device?

It's the first time I've used an aircard, having previously used standard hotel wi-fi. Can anyone offer any advice on resolving common mistakes or pitfalls with such a device?

No. The microsd slot is for convenience only. You can use the modem as a usb key to save files, as well as a modem. You can just leave the slot blank.

Thanks jackbox, much appreciated. I have a Western Digital passport external hard drive for the laptop so I won't bother getting the micro SD card for now.

As said just an optional little back up for if you are downloading a file and want to store it somewhere mobile. I stuck a 2GB one in mine and it comes in handy.

Since the stick uses a USB slot, and for some those might be limited, many manufacturers have started offering this uSD flash option.

In the OP's case they might consider a 3G SIM from TOT or one their MVNOs like i-Kool, IMobile. This stick, I'm pretty sure - there are several models all with different radios - supports 3G:900/2100, so a fit with TOT, which likely has coverage in the area where the hospital is. TOT have 3G coverage maps on their web site. They have ~ 600 base-stations in metro-Bangkok; I have coverage from four base stations. If 3G is not a requirement then many mobile phones have 2G (GPRS/EDGE) modems and can be tethered to a PC thus obviating the need for a USB stick.

Also check to see if it is OK to use GSM/3G radios in the hospital; some forbid it. Finally, True and others have great WiFi coverage so this may be an option depending on the hospital.