Can you get a Sony ericson Z750i unlock code free?

No but you can unlock it without a code and with a patch here:

Sony Ericsson Phones Supported:

C510, C702, C901, C902, C903, C905, G905,

G705, K630, K660, K850, K858, T700, TM506,

V640, W595, W705, W715, W760, W890, W902,

W908, W910, W980, Z750, Z770, Z780

Instructions:

2. Download this program located here: http://www.megaupload.com/?d=PR9VXTIV

3. Open the program and go to settings and type in the account info below (DO NOT CHANGE ANYTHING ELSE)

4. Select your phone model and press unlock and follow the instructions and wait for the message

"The action reported success"

5. Enjoy your unlocked phone

*Account*

User Name: PSPdownloadS

Password: Flybonez360