Your comment is really quite ignorant.
Wi-Fi has many advantages over 3G and HSDPA in terms of speed, and reliability to name just a few.
Businesses that have WiFi LAN’s and WAN’s setup for sharing their intranet, storage servers, exchange servers, are behind a firewall and cannot be accessed over the internet even using VPN use it with their laptops and mobile devices.
If your device has WiFi and HSDPA then using appropriate software you would be able to make your phone into a mobile WiFi router, and connect a laptop to the internet in an emergency.
At home, WiFi can be used to stream video, audio, share NAS drives, and printers, the list goes on and on.
Additionally, you might live in an area that has no 3G coverage, then you’re stuck with GPRS or nothing, but if you had a wireless router at home, then that’s not a problem.
Finally, if you’re on a legacy tariff or cannot justify the additional £7 per month for Web & Walk as it’s only for occasional use, then WiFi is a free option, assuming you have access to a WiFi network.
Do you want more reasons?