Samsung GT-I9100 004999xxxx imei repair done by z3x box free here
 Download multi firmware from HERE
Success Fully imei repair done in z3x box 
How to repair imei in i9100 from the z3x box:- must your mobile have to rooted
 - must enable usb debugging on in your mobile
 - must your mobile on lets start
 - connect your mobile in pc via usb cable
 - open z3x tools
 - click on Repair button (must click on "USB model")
 - fill imei legally
 - click on ok button
 - you are done 
 
Note : if any problem in unlock just write down query in below comment box i will soon reply you 
logs:
 Selected model: I9100  
 Selected port: COM5 Z3X BOX Serial Port  
 Selected port speed: 115200  
 Phone not found  
 Done with Samsung Tool v.15.4  
 Selected model: I9100  
 Selected port: COM5 Z3X BOX Serial Port  
 Selected port speed: 115200  
 Reading phone info...  
 Model: GT-I9100  
 Android version: 2.3.6  
 Product code: Not Active  
 Phone version: I9100XXKL1  
 PDA version: I9100XXKL1  
 CSC version: I9100OXAKL1  
 IMEI: 351534856897635  
 Phone S/N: 00000000000  
 Checking Super user right... true  
 Reading data from phone... OK  
 Unlocking... OK  
 Rebooting phone... OK  
 Unlock done  
 Done with Samsung Tool v.15.4