http://www.pcworld.com/businesscenter/article/181590/verizon_droid_tethering_will_cost_you.html
That $30 a month buys you an 'unlimited' data plan that has a monthly cap of 5Gb. Clearly, we are using different dictionaries to define 'unlimited'. Something got lost in translation somewhere.
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Verizon has confirmed that tethering will cost you though--an additional $30 per month for an additional unlimited data plan that is also limited to 5Gb. So, if you want tethering you will pay $60 above and beyond the monthly contract for service for an 'unlimited' 10Gb of data per month.
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But wait, there's more! That $30 a month data plan grants you the ability to use an 'unlimited' 5Gb of data...as long as that data doesn't come from a Microsoft Exchange email server. If you want the privilege of connecting with an Exchange email account you have to pay $45 a month for the 5Gb of unlimited data.