I feel like there is a major misconception about phone technologies in the United States (this perhaps would exist in Europe if they didn't all use one protocol...). Let's be clear---there is no "hacking" your way into the iPhone using Verizon.
AT&T and T-Mobile (and a few regional carriers) use a protocol called GSM (Global System for Mobile communications, formerly Groupe Spécial Mobile), a protocol jointly developed by a bunch of European countries to standardise interoperability of mobiles across different countries. The data protocol that operates with GSM was originally GPRS. Both of these technologies represent 2G technologies. An effort to increase datarates before 3G technology roll outs resulted in EDGE (Enhanced Datarates for GSM Evolution).
Verizon and Sprint (and I think AllTel) use a technology developed and patented by Qualcomm called CDMA (Code Division Multiple Access). This is to differentiate it from the 2G technologies of GSM, which use TDMA (Time Division Multiple Access). CDMA vs TDMA is where the fundamental difference between the two protocols can really be seen. They are both strategies for sharing a radio spectrum across multiple connections. These methods literally involve different hardware requirements. Therefore, you will not see a software hack to the iPhone that makes it work with CDMA. There are fundamental differences in hardware and firmware needs between the two technologies. Furthermore, the data protocols adopted by CDMA carriers were 1xRTT and EV-DO. These are, once again, completely incompatible with GPRS and EDGE technologies.
In terms of 3G, EV-DO is considered a 3G technology, and the CDMA carriers have invested a fair amount in it. The 3G protocol adopted as the bolt-on to GSM protocols has almost universally been UMTS (Universal Mobile Telecommunications Systems), a protocol with an easy roadmap to add HSDPA, a high speed download system developed to enhance UMTS. They have also begun to develop similarly divergent 4G technologies, so even if their bandwith sharing strategies converge, it is unlikely we will see any easy interoperability among carriers (aside from certain phones, like the Blackberry 8830, which literally has both CDMA and GSM hardware smashed into it, at the cost of a fair amount of miniaturisation and likely battery life, though I'm not sure about the latter). All other phones will only operate with ONE of these sets of protocols (though a phone company may release different versions of the same model, they are definitely different "under the hood").
Until then, you will not find me anywhere near an iPhone.
