AT&T Tethering as we have just found out is going to cost an additional $55 per month with MMS coming in July.
Although this is a rumour via the internet I am sure you will agree this is quite expensive although MMS is rumoured to be launched in mid July which is much more plausible. Hardcore iPhone fans like yourself will know that places like Austria get tethering for free and Nordic countries have unlimited data that allows tethering for less than $20 a month (this has been going for several years).
If you want unlimited 384kbps in Finland this will cost you $14 which is fairly reasonable. This info at the moment is not totally official as of yet and AT&T have a way of bending to the demands of the Apple iPhone mobile.
Source — App Modo