Hi there, and welcome to JustAnswer, I look forward to assisting you today with your question and providing the best answer possible.

The SMS messages are stored on the SIM card on your phone (not on the phone itself).

To retrieve deleted SMS messages the first thing you need to do is stop any sending and receiving of SMS's) The reason is that the deleted SMS messages are still on the SIM card, but if they are overwritten with a new message, then they are gone for good.

You will then need to buy this SIM USB reader so that your SMS messages can be read by a computer

http://www.dekart.com/products/hardware/sim_card_reader/

You put the SIM card into this reader and put it into a computer.

You will then use the dekart program Sim Manager

http://www.dekart.com/products/card_management/sim_manager/

It will retrieve deleted SMS messages on the SIM that have not yet been overwritten. They will then be available on your computer

If you require any additional information, please do not hesitate to let me know.