You can use Threaded SMS (I think its ported by CodyPPC) or you can try a new one called something like xtreme threaded SMS. I think its still on the front page of the software forum.
Extreme Text Thread http://forum.ppcgeeks.com/showthread.php?t=12534
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OLD SANYO PHONE -> OLD LG PHONE -> SAMSUNG N400 -> SANYO 8200 -> SAMSUNG A900 -> SAMSUNG A900M -> PPC 6700 -> MOGUL -> TOUCH PRO -> HERO
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