The proposed iPhone plan sounds familiar, as all the cellular broadband plans I have researched have turned out to be almost identical in two key areas:
Total cost is $60/month for "unlimited" (device does not matter - if you have a smart phone, you typically a premium to your plan for data access from the phone. To tether it, the add on cost for unlimited data almost always brings the cost to $60/month. This is the same $60 for a full plan on a dedicated device.)
"unlimited" means 5GB data transfer per month. (Yes, even Sprint has gone this route now. Quite disappointing.)
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I have yet to see a cellular broadband plan (which means dial up to 2M speeds typically) cost less than a classical broadband plan. Then again, when I went on vacation, I wasn't able to access my cable internet while traveling. However, being able to jump online when in an unfamiliar region to hunt down services (gas prices, where the nearest drug store is, where hotels and auto repair services are, and so forth) was a life saver. Add it the ability to "e-Commute" to work on bad weather days (or when waiting for the cable guys to come by and fix the system... again), and for my $60/month is well worth it.