I am very disappointed that Verizon does not offer a unlimited data card plan, or provide options for users to help control bandwidth.
Virgin Mobile offering data card service, unlimited, for $40/month now.
T-Mobile and Cricket offer 5gb plans, but promise no overages. Instead... they will simply throttle speed if the limit is reached. They will not stop service or charge you overages.
I will happily pay the early termination fee to save $20/month on my wireless internet costs and no longer have to worry about how much bandwidth I use. (This is of higher concern to me since I often use my air card with a router to share internet with a few people around me).
Not only is the coverage an issue, you also have to be careful and be aware that unlimited may not be "truly" unlimited at least on any long term basis. If you were to use over 20GB per month, (or whatever their Red Flag usage amount is) it is more likely than not that you would hear from them or suddenly experience slow speeds or connection problems without notice.
There is a national fair usage policy which gives the carrier to excerise their right to do what is necessary to provide the minimum connection quality, etc. to all users if it becomes warranted.
The carriers don't think of the service as a primary source for a family to access the internet. The service is designed for a secondary or intermittent use so if the monthly usage is over a certain amount and continues to be that way every month or a high percentage of the time they may have an issue with that down the line.
The network/tower space leased for each carrier has a limit on how much bandwidth can be provided at a given time so if the "unlimited" usage on any given tower at the same time of the day has more demand than it has bandwidth to be provided, then you and other users begin experiencing problems that can only be corrected by dividing that capacity between you all.
However, enjoy it while it lasts and in this economy any savings is definately the more attractive option. Just don't get your hopes up that it will last forever.