Google Voice texts delivered hours late/not at all
I'm not really sure why it happens, but I've experienced the same issue in the past with the very same phone.  It usually happened when I was travelling, such that once I arrived at a new destination, I'd suddenly get text messages delivered.  The issue did seem to go away when I installed a custom rom (the latest Cyanogenmod at the time).  I've since gotten another phone and have never experienced the issue.  If you're feeling brave, I recommend flashing a newer rom.