This phrasebook is a most useful book for anyone wanting to travel in Iran, or for any student of Persian (Farsi is the language's Persian name).
The scripts are done quite well. Each English phrase has two Persian equivalents, a colloquial Persian in Latin ('English') script and a formal written Persian in Arabic script. For example, "Do you speak English?" has the colloquial "[shomâ] ingilisi balad-in" in English script and the formal written "[shomâ] ingilisi balad-id" in Arabic script. The colloquial form is the one to learn, unless you want to write something. But the Iranian or Afghan you show the Persian phrase to will see the formal written language he or she expects to see. Just be aware that if you ask someone to read out the Persian script, it'll probably be slightly different to the Latin script (only slightly - the colloquial isn't Persian slang).
Both of the phrases are always in the polite form (shomâ) rather than in the intimate (to) form. Iranans are a courteous people and the polite forms are always best except with good friends or family.
There's lots of information on how to behave, on body language, a little grammar at the beginning and a mini English-Persian/Persian-English dictionary at the end. The only section it doesn't have is the usual Lonley Planet 'Dating' section, which is probably just as well ("it isn't considered acceptable to date an Iranian" as it warns you under the "Arranging to Meet" section).
If you're travelling further East, and need to use the Tajik dialect of Persian, try Central Asia: Languages of the Silk Road (Lonely Planet Phrasebook)