However, my new phone- the above-mentioned Samsung Epic 4G- does not offer this option. There is an app available in the market called Roam Control, that allows this feature if the phone is rooted. However, if you live in Florida, most of Texas, and a few other places that Verizon doesn't have coverage in the 850mHz band, Samsung won't roam. Damn....
Well, I like a challenge. And I have found a way around this (and it doesn't involve hacking PRLs)
There is an NV item in the phone. 00442- nv_roam_pref. Using QXDM (QPST or NVEditor might work but I didn't try. NVEditor doesn't list it- it'll have to be added, and I didn't check QPST), change the value to 0x0002. And to answer your next question- Google is your friend!
[EDIT on 11/8/2011: QPST doesn't list this NV item, either.]
Here's a screenshot:
My phone is showing 3-4 bars now (0 to maybe 2 before). The roaming indicator is on, I am able to make and receive phone calls, send and receive texts, and browse the web (1xRTT only- showing about 100k). And the change seems to be persistent after reboots. I was able to revert it by changing my Network Preference back to 'Sprint Only'.
Now- if someone can write an widget that does this, that can be repayment to me for the time and effort I wasted trying to figure this out. Here's a middle finger to you, Sprint and Samsung!