Recent cellphones have the option to protect a memory card via a password, but in case you forgot yours and really need to use it again, just buy this useful accessory.
It connects to your computer thanks to the USB port, and can unlock different types of cards, such as SD, Mini SD, Micro SD and MMC. The working method is as simple as it can get: just plug the card in, and wait for the red LED to start blinking.
The USB Memory Unlock costs $16.
This SD/MMC cannot help you to get back the data (otherwise, your data will be quite danger), but it can help you to unlock your SD / MMC card so that you don’t need to buy another one.