One of the features of the new iPhone OS is screen orientation lock. Like the iPad this prevents the iPhone moving into landscape or portrait mode when the lock is on. With Apps such as iHi Translate that work in both landscape and portrait this can be a useful feature.
The orientation lock is shown a padlock inside a circular arrow at the top right of the iPhone screen. A problem many people have encountered is how to switch this off. Most will naturally look through the "settings" and not be able to find a way to switch on or off the orientation.
The way to lock or unlock is by using the multitasking feature. Double click on the home button to display the Apps. Then scroll as far left as you can go and you will find the screen lock/unlock. Press once to move from locked to unlocked.
We hope that's helpful and will let you use the world's phrasebook iHiTranslate in which ever orientation you prefer.