Yes a few people have managed to get 3g working be it with the pcmcia credit card type device and then using DUN or via a handy with 3g on it.
The handy / mobile / cellphone with 3g and dun might need a cable or bluetooth or infra red connection and possibly some software or modded software to do it.
Just google for " 3g linux " and you should find plenty links. As for Gentoo based it is just a question of getting the source code and compiling.
I know for some of the sprint cingular type you will need drivers or firmware same as with a wifi card and ndiswrapper , might get away without sprint / t-mobile software
Several of these wifi 3g data card is made by 2 or 3 company's so it is not too hard to find it or get a generic one that works for most of them.
They have had this 3g phones and data cards for 1milj years in Europe already so try google.co.uk or ?? google.eu and the germans has figured most of these things out already.
PS> google.com will limit results to USA only = no answers unlike it is on google.co.uk for UK / Europe = answers.
To unlock the nokia phones use this link as your service provider is supposed to after 6 weeks / months give you this unlock code or you tell them you are going overseas and you want to use a local sim card , then they have to unlock your phone .
Also if all else fails with the phone being too old technology try to get a 3g data card on ebay they go for $40 - $50 unlocked ie: can use it with any of the jokes for mobile company's here.
Merlin , novel / novatel is mostly the manuf. and they rebrand it as sprint vodafone t-mobile here.
Look for the ones that can be firmware updated to 7mb/s
PS> I am not trying to bad mouth the company's here but they are so far behind that all the old junk the rest of the world can not give away for free ends up here as NEW tech. and extremely expensive.
Hope this helps.
THis is a pain as I was looking for this a while ago as well and came to above conclusion.