...it's not possible for a virus to be spread via e-mail or network connections so you should be completely safe.

Seriously?!? I'm not up to date with mobile handset virii but I would imagine that plugging into a laptop via USB could transfer an infection.
Basically, with a 3G connection, your phone is connected directly to the Internet (probably behind NAT or whatever unless you have a special arrangement with the carrier for VPN). If there's no current exploits for mobile browsers it's probably only a matter of time before someone embeds malicious code onto websites.