OK! After experiencing such deleted data loss troubles a couple of times, I have learned whether you can recover your deleted files from that Android phone often depends on whether you do save these original data on the HTC phone memory
card.
If you do save them well there, without data backups elsewhere, you do have chances to get them all back with deleted data recovery software, like:
http://en.wikipedia.org/wiki/Data_recovery
http://www.icare-recovery.com/free/undelete-files-sd-card-freeware.html
But, if you do save them all on the phone internal memory, the answer could be completely different.
So, always save one copy of important phone data on the phone memory card and also make data backups well.