Wireless-G Router for Mobile Broadband
The Linksys Wireless-G Router for Mobile Broadband is really three devices in one box. First, there's the Wireless Access Point, which lets you connect both screaming fast Wireless-G (802.11g at 54Mbps) and Wireless-B (802.11b at 11Mbps) devices to the network. Second, it’s a built-in 4-port full-duplex 10/100 Switch to connect your wired-Ethernet devices together. Connect four PCs directly or attach more hubs and switches to create as big a network as you need. Thirdly, the Router function ties it all together and lets your whole network share a Mobile Broadband Internet connection (requires a Mobile Broadband Data Card, available separately). You can also use a standard Ethernet attached Internet connection, like a cable or DSL modem, if available.
Once your computers are connected to the Router and the Internet, they can communicate with each other too, sharing document files, a printer, storage space, and other resources.
To protect your data and privacy, the Wireless-G Router for Mobile Broadband can encode all wireless LAN transmissions securely with WEP or WPA Personal encryption. The Router can serve as a DHCP Server, has a powerful SPI firewall to protect your PCs against intruders and most known Internet attacks, and supports VPN pass-through. Configuration is a snap with the web-based configuration utility.
With the Wireless-G Router for Mobile Broadband, you can create a secure wireless network with Internet connectivity, anywhere that Mobile Broadband Internet service is available.
Linksys WRT54G3G, White
Linksys WRT54G3G. Network standard: IEEE 802.11b, IEEE 802.11g, IEEE 802.3, IEEE 802.3u. Product colour: White, LED indicators: Power. Certification: FCC, Wi-Fi. Weight: 350 g. Dimensions (WxDxH): 170 x 170 x 33 mm, Minimum system requirements: -400 MHz or Faster Processor -128 MB of RAM -Internet Explorer 4.0 or Nets for Web-based..., Maximum data transfer rate: 0.1 Gbit/s
Allows you to share your 3G network with colleagues... 
Large, even larger power pack, difficulties setting up, connection costs... 
As an ad hoc network at a conference or trade show youll be hard pushed to beat it as long as you can afford the connection fees...