"Flashing to Straight Talk" can vary, depending on how you want to go about it... Straight Talk has two types of service, CDMA and GSM, both of which will work on the Rezound to a varying degree.
The CDMA mode is as @mjones73
mentioned, and it required a donor phone to clone the ESN/MEID from to be activated. This will use Verizon service in 3G mode, which is kind of slow (about 600kbps in my area at best) but it will work. The practice of ESN cloning is... umm... questionable though technically possible.
The GSM mode requires a stockish global mode ROM, and a T-Mobile or AT&T SIM card from Straight Talk... Voice and SMS will work out of the box, MMS and data require a little tweaking. There are a few guides out there but @REV3NT3CH
is working on a guide to get AT&T 4G on the Rezound... yes, I said 4G! I believe he also has/had 3G working on T-Mobile service with Straight Talk as well. Be patient, those guides will be coming soon, I know he is working on them and they should be ready soon.
Current Personal Phone: Google Nexus 4 on Cricket/Aio (Beanstalk
4.4.4 with hells-Core Kernel
Current Work Phone: LG G2 VS980 on VZW (Official Beanstalk
Current Tablet: iPad 4 and Samsung Galaxy Note Pro 12.2
Other phones "in the family": HTC DNA, HTC One (M7), Motorola Moto G GPE
Previous/Retired Android Devices: HTC Aria, HTC Incredible 2, HTC Rezound, Samsung Stratosphere, Samsung Galaxy S2 Skyrocket, Nextbook 8P