Curiosity or jealousy, an innocent prank or specific surveillance - no matter what reasons pushed you to read your husband's SMS, you thereby grossly violate his boundaries of personal space, which means you do not respect him. Consider whether 5 minutes of satisfied curiosity is worth it to possibly lose your spouse's trust forever.
Read letters on your husband's phone without risking losing trust
You can read SMS on your husband's phone only if you have informed him and he has given you his consent. It is better that this event takes place in his presence, and he knows exactly with what motives you are doing it. If your motives are so innocent that you can safely tell your spouse about them, then - of course, why not. You can even send messages from his number to his friends, girlfriends or colleagues, if only he explicitly allowed you to do this.
If you are driven solely by jealousy and a desire to secretly find out the details of the spouse's alleged personal life with other women, this is already a very bad signal. Your beloved man is not your property. You cannot control it like a trained dog. And if you can, then nothing good will come of it for sure, and it is still unknown who will be worse from this - him or you. Keep in mind that such an invasion of someone else's "territory" is a sign of clear psychological failure. By the way, if you do the same with your children, especially teenagers, they may not forgive you for this. Every person needs personal psychological space.
What to do if you suspect your husband of infidelity and therefore want to read his SMS story
The surest way is to directly tell your spouse about your suspicions and "call" him to account. If he has no intrigue on the side, he will probably tell you about it. Of course, he may be deceiving, but then only your experience in communicating with your husband can tell you whether he is deceiving you or not. But if he begins to evade an answer, shows excitement and uncertainty and starts hiding the phone, this can serve as a signal that he really has something to hide from you. Moreover, if you, for example, noticed that at night he systematically receives some letters, and you are sure that this is not an advertisement …
What other situations allow you to read SMS on someone else's phone
There are no rules without exceptions. So it is here. In extreme situations, for example, when your husband suddenly and for no reason disappeared somewhere, and his phone remained with you, the boundaries of personal space are slightly inferior in relevance to other, more significant things. The latest messages on the phone, perhaps, will help both you and the search services to find the trail of the missing person.