I think there is curiosity then there is snooping...
Curiosity takes over 1 in 10 times u will be alone with your partners phone. Its that one time you just read a text or check the logs, just to check whats goin on in your partners life, its not about catching out or suspicion. Its almost just pa**ing time.
Snooping on the other hand is filled with suspicion, its about catching someone out. By the time you get to the snooping point in a relationship, just Know you have problems. Even if you did not find anything, you wont be satisfied. You will try harder to find something, it will consume you. Snooping fuels your existing insecurities. It will make you the person your not or would want to be.