Known issue with all 1.5 CDMA devices. It gets even worse. Using this bug anyone with your 10 digit number can kill the SMS database on your phone and require a hard reset for it to ever work again. It's fixed in later releases.
Out of order texts -
Timestamp issue from your local towers. Sprint has to have accurate timestamping because they also carry the internet data for the US gov't on their backbone. Data packets (SMS/MMS data, not data data
) sometimes get held while trying to verify 'incorrect' timestamp signatures. If after a certain amount of time no refreshed packets with the 'correct' timestamp are received the tower programming stamps it with local time and forwards it down the line. Only towers with a bridged PCS/backbone connection are affected, and only when receiving data from non-bridged towers. It's hit or miss, but fixable.
Simple answer - your texts take a back seat to Internet/VoIP/other 'real-time' data.