Pre-paid is pre-paid, regardless of what ph you choose. If you're looking for a state of the art model like a Galaxy S II with a pre-paid account at the carriers (bundled deal), you're about out of luck. Well, not about, but totally SOL.
If you want a slide out keyboard, and still keep a large display, then you should look for something like a desire Z or the carrier based equivelant. You won't find it in a bundled pre-paid package. These were, and still are in most cases, considered a premium phone.
Of course, if you wait till Nov, the christmas line will come out, so you might see 1 or 2 models added to the low budget pre-paid lineup. Maybe. But they won't be premium phones for under $200.
Most of the "unlocked" gsm phones, will get 3g in most countries. Mine, has no issues.
And if you're "broke" and on a limited budget, I don't think you;'re concerned about 4g, 4lte, 4ltd, super4, or any type of 4g network, because you can't afford the data plan. Besides, your prepaid, well, only works on 3g.
Unlocked, means unlocked. And they will work on 3g networks, exactly what budget pre-paid phones do. But you will have a much better phone in the long run, to purshase a used great phone, versus a POS cheap phone.
But hey, if you wanna buy cheap, expect cheap