Is there a possibility to recover all the deleted messages from cellphone to solve a crime? How?
Yes it is so possible. There are a lot of commercial software out there that does that. When you delete a file from a memory card, it wasn't really deleted like what we expected. The space occupied by the file will be marked with special marker like 0’s or any character by the system. Marking depends on the algorithm used to it by the vendor. When you save another file it is possible that it will be stored in the newly freed area but the old one does not go away. Special softwares are used by the crime investigating agencies to scan storage. So if you think that it is permanently gone, you're wrong. You can search over google to find some of this type of software. Most of them are for sale but you can get trial and try it on your cellphone or any device.
Yes, I think it’s still possible to recover them but that is if the phone is set to use the memory card for storing the messages it receives. The memory card is very similar to a computer’s hard drive or a USB flash drive. And these types of media are very capable of recovering deleted files using different file recovery software. But I’m not sure if it’s still possible if the phone was still set to use its internal memory for storing the messages since most file recovery software on computers seem to be incapable of accessing the phone’s internal memory.
Even if the files to recover are located in the memory card, it still doesn’t guarantee that all files can be recovered and undeleted. If the deleted files were overwritten by newer files, recovering them is no longer possible. If a file was deleted, any new files copied on the same container will replace the information of the previously deleted file. That’s why it’s very important not to copy new files on the drive after an accidental deletion to have a high chance of recovery.