Virgin Mobile (as far as I know) runs on Sprint's network. OP will have a GSM mobile, so he'll need either AT&T or T-mobile. I think T-mobile probably has better prepaid offerings.

I think the OP will want T-mobile's Pay by the Day plans, since I don't see data included in the above link. http://prepaid-phones.t-mobile.com/p...ll-phone-plans

OP - just walk into any store in Manhattan whose outside sign does not say something like "Authorized Reseller" or "Premier Agent". It should just say AT&T or T-Mobile. Those are the corporate owned stores, and they will not try to sell you needless add-ons. You can also just go to Tmo's website and use the store locator. Pick any Corporate store.

As for clothes...the USA is roughly the size of Europe. You will encounter a variety of climates and weather. Though, as I recall, you're coming in summer. Expect the east coast to be hot and humid. Expect Arizona to be hotter (temps above 40C are expected) and dry. Expect LA to be warm and sunny (20-low 30s C).

San Francisco has a microclimate all its own, because it's on a peninsula surrounded by cold water. It will be in the teens C, likely overcast or foggy, and you will want a light jacket. But if you drive 20 minutes in any direction out of the city it will be hot and sunny.

I use a subway app for iOS called Embark NYC Subway. Hopstop is another good app for directions in Manhattan. But for general directions (including Manhattan), Google Maps is all you need.

As for flying from LAX or LGB ...depends where you'll be and available transport options from there. Alaska and JetBlue are two of the nicer domestic airlines.

In general, you will find US and UK culture remarkably similar. I think Americans tend to be more overtly friendly to strangers; we lack that British reserve. You'll have a great time. If I'm in town, we could even meet for a beer. PM me if you'd like.