Same thing has happened to me. Seemed to happen around the end of October. I have a BOOST phone and a BOOST sim. BOOST have been zero help and some of the missing messages relate to a legal matter and are important evidence. I don't think BOOST wants to admit they have a security problem. Have you been in touch with BOOST? They promised to send a record of just the date the texts were sent but are now refusing. Seems to me they have a security issue that they don't want to admit to. Someone else told me it could be because they are old messages but the messages are from late last year to about May this year and other much older messages have not gone missing. Interestingly the first 2 messages are there and all the others are gone. I am considering going to the Ombudsman. Evidently it's impossible for this to happen so it is interesting to see that I am not the only one. Now I wonder how many other messages went missing.