Update: This mobile Wi-Fi (MiFi) solution is now available in Malaysia, and is offered by Digi. Read the June 4, 2010 news item.

Update: Here’s a post with photos showing the iPad being used with the Digi MiFi solution. Read more at Eric Yong’s blog post.
If you want ubiquitous internet and data access for your WiFi-only iPad, one way is to carry around a portable, battery-powered modem / router which allows you to slot in a SIM (or micro SIM) card with cellular broadband data access, and have that device create an instant WiFi hotspot that your iPad can connect to.
This would also be a good solution for times when you want to provide WiFi access for a group of individuals with their own mobile devices, or when you’re traveling on the road in a vehicle with family and friends, and each of them has an internet-capable mobile device and wants to access the internet.
Simply switch on the portable WiFi / Modem router dongle and you’ll have a WiFi hotspot that everybody can connect to.
Here’s a (growing) list of said device.
HUAWEI E5/IMO/I-MO/E5830 USB WiFi ROUTER/MODEM UNLOCKED

Find this on eBay, and read this forum thread for more details, larger images, and an excellent description of the device.