Why do you need wifi or even 3G on a Blackberry?
It would be a boon if we had 3G or WiFI enabled blackberries!
The company I work for relies heavily on the Blackberry for general out of office / not at desk email manipulation, the extra speed permitted by 3G (probably about 1.4Mbps) would allow quick downloading of attachments, etc.
Also note that we use our blackberries as modems too, so if I am out of the office and I am called out, provided i have both my laptop and blackberry, I can easily give my laptop a 'net connection wherever I am, again this is sped up by the 3G connection.
With regard to WiFi, this is useful in a LCS (Least Cost Routing) solution. So, say for example you arrive in the office, rather than using the mobile network, the blackberry senses the corporate WiFi is in range and calls switch to this (with some jiggery pokery in the backgroud to handle the call diversion) but either way it saves costs. We already have some inhouse solutions which do overseas calls and utilise company bandwidth instead of the mobile network which is quite successful.
Finally, from a remote worker perspective, using the wifi means that the blackberry can act as your 'desk phone' wherever you are. Blackberry senses your wireless network, logs on, registers remotely with the company network servers, and calls are routed to your blackberry (virtually) toll free.