Custom ROMS... Will sprint get mad?

[amd4me]

Sprint is pretty cool about it. Verizon on the other hand flips their shit if you do anything to your phone. The lady at the Verizon store in Santa Fe tried to void my mothers warranty because she wasn't using a Verizon approved car charger.

[Skytso]

As another tech said already... It's really not a big deal. I would recommend flashing back to the stock ROM, just in case you get that one dbag that has way too much company loyalty. Re-locking the device is just a pain and I seriously doubt anyone working on your phone in a Sprint store would be able to tell that you've unlocked the phone. I mean, I know I wouldn't be looking for it on the average person's phone!

I'm not entirely sure your warranty would be void if you just send it back to Sprint... Honestly, I don't think they'd actually do anything about it. But I definitely wouldn't chance it, just in case you get that one retard. =P