Unlimited/unmetered is a hard thing to offer. First off, you can never technically offer unlimited bandwidth, so stating you do is a lie. However you can offer unmetered, but you run the risk of your customers using enough to lose money, and in that case you won't be able to continue doing so.
I completely understand why people want unlimited/unmetered. For the most part it's because they don't want to have to worry about overages, but most don't actually know what they'll be using until their sites reach higher popularity. http://www.fiberelephant.com
only averages 200-250GB bandwidth a month. We do quite a bit of file transfers between clients(ticket attachments, software downloads), and http://www.tjphippen.com
So while we would love to offer unmetered, it's really not necessary. I personally suggest purchasing a VPS with limits, even a smaller plan to start out. Then as your traffic ramps up you'll be better able to gauge your needs.