I've been messing with NRG's ROM 23518_Jan_20_LEO Maxmanila and guess what, out of the box messeging just plain works. SMS is instant MMS take a bit to recv on the end ( about 5 Min) but it works without any patches or tweaks. MMS file limint is set at 300k but when you install and run MRX Provision and PRL cabs for Sprint its bumped upto 1000k (Sprint server limit) I can only speak for the Sprint TP2 and Network.
MRX downloads below:
http://forum.ppcgeeks.com/showthread.php?t=96207