I think you should go for the first school policy about phones. Students should be allowed to bring cell phones to school but only to be used during their free time. The reason why is that if you ban phones from the school than students might not really care and they will just bring their cell phones anyways. On the other hand you should also warn that their cell phones could be brought in and used only in their free time. You can also warn that cell phones will be confiscated if students are found using them in class.

The main reason is because they wont really care if cell phones are allowed and you don't really do anything about it. The more this happens, the more they will get used to it. If cell phones are just banned then they will still do the same thing, only they will use them more often, behind the teachers' back. This is why you should allow them the freedom for cell phones to be used only in their freedom. That way they know when and what will happen if caught. Otherwise they will continue to use phones in class if they are not confiscated until the end of class. If the phones were to be confiscated for a longer period of time, than maybe the students will start using them less and less often in class. The policy should have other things added in like for phones to be confiscated for long periods of time, consequences, and or like the contact of parents if caught using phones in class. This will not only get them in trouble in class but at home maybe, if not they will not learn. If they do manage to realize, than they will do better in the future or think better of the consequences.

Basically you should allow cell phones but with not so many heavy punishments that they will continue their previous acts with out caring. You should still have consequences and warn students of confiscation for long periods of time. This might make them use phones only during recess or lunch or other free times available to them. In the time being of the confiscation they will think better of their actions and therefore act better of it.