How to Install iPhone OS 4.0 Theme? Your device must be jailbroken. You must have Winterboard installed via Cydia. You must have ModMyi Repository added to Cydia. Search for iPhone OS 4.0 in Cydia and install it. Launch Winterboard and activate iPhone OS 4.0. Screenshots You can also search and download OS 4.0 Calendar icon from Cydia to match this.