I'm afraid that if a message has been deleted then it has been deleted. There is no "trash can" you can retrieve stuff from (i.e. stuff that hasn't been deleted, just flagged for deletion). And surely someone doing this on an iPhone would empty the trash anyway to make sure you couldn't recover them? (I don't know iPhones that well, but I'd certainly try to make sure stuff was really deleted if I were in this person's position).
You could install a message backup app so that you had a copy of any future messages. SMS Backup+ can be set to automatically back up messages to your GMail account, and you can set it to do so when messages are sent or received, so that should let you keep a record of any future texts.
Retrieving photos depends on what model you have and where the photos are stored. Pictures on an sd card are easy - mount the card on a computer (use a card reader if the phone doesn't support USB mass storage) and use file recovery software to retrieve deleted files (I've seen Recuva recommended for Windows). But if you have a Nexus then you can't do this (no SD card), and you won't be able to run file recovery software over the MTP interface that they use to connect to a PC, so to be honest I doubt you can recover pictures.
Again, if it's picture messages then a message backup app might help in future. If camera shots, maybe if you set up automatic syncing of images to some cloud service (Dropbox, Picasa, etc) that would work.
Or, another thought: I just came across this on the Play Store -
https://play.google.com/store/apps/details?id=com.baloota.dumpster. Again, won't help with stuff that's already gone, and actually I've just spotted that undelete SMS is "coming soon", but it might be worth investigating in future.
