Hi,
The only difference between the 8800 and the newer 8820 is that it has Wi-Fi. Normally you should find no price difference between the models so you would be best to purchase the newer 8220 or hold out a few more weeks for the BlackBerry Bold (a.k.a BlackBerry 9000). When it comes to using Skype on BlackBerry there is no client actually make from Skype so you will need to use a third party product. For some examples please refer to the links below:
iSkoot | Life on the go.
IM+ for Skype :: Products
Thanks,
Gary