The gap for more "advanced" plans is even more egregious; Wal-Mart+T-Mobile US is providing a pay-as-you-go plan for $30/mo with unlimited (5GB throttled) HSPA+ data+SMS and 100 minutes of voice. Over two years, the plan itself (assuming no overages) works out to about $720. Ignoring the cost of the phone, Verizon's most comparable plan (400 minutes voice, 5GB data, unlimited text) is $140/mo, or $3360 over two years…
T-Mobile's prepaid network is smaller than their general network (or so the reps told me)
The rep lied to you, he wanted to sell you postpaid. Better commision for him.
Network-wise, the difference is in the billing backend, not in the towers or coverage.