They're just slapping on a more sophisticated name for a remote unlock. There are no such things as frequency unlocking. A device's baseband chipset has a predetermined set of radio frequencies that it can receive, there's no way to 'unlock' it without swapping it out, which is illegal. then you have the world model phones which universally support all bands, so unlocking for those are just unlocking for recognition of other carriers is all.
Frankly it's not worth the price for an iPhone 4. The 4S and above are worth unlocking, especially the world models, because the specs are better, and they have better radio frequencies to support HSPA, 4G, LTE, etc. and if your iPhone 4 is already on AT&T, you can already use AT&T prepaid SIMs, there's no need to unlock an AT&T phone to use it's own SIM
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