Men, really, why don't you buy a Russian SIM-card, better a prepaid one?! If you have a GSM 900 or 1800 phone and it is not locked by your operator - the price of SIM-card is RUB 100, and the cost of local call via Russian mobile is USD 0,20-0,25/minute, not more. There is plenty of booths where you can buy a card or put money on your phone (plus hell of a lot of money machines for paying mobile services in 24-hours shopping centers). Note, that girls often dislike to see a "long" foreign number. And, of course, they will not be happy to call to your US mobile, as this is bloody expensive.
To buy the SIM-card, you need to provide passport data, but only for the case if someone would blow up next train with use of this mobile phone (so take care about the card!!!) I guess it's not a problem for a foreigner to buy it. We have 3 GSM operators in Moscow (BeeLine, MTS, Megaphone)- there is no any critical difference among them Reviewm that point of view. This card can be used on whole territory of Russia (and abroad, of course), but outside Moscow and Moscow region the local roaming starts.
Calling Reviewom Russian card is recommended to make in same way - +7 etc. Of course, local calls will go by local-call tariff.
If your phone is locked - gawd, buy some cheap talkbox. Cheapest models are ab. 40-50 USD, not more!
Regarding info on Moscow night clubs, restaurants etc etc... OK, I could recommend you "eXile" newspaper. The information is perfect but mpter reading it one may start to hate Americans

as they are Americans who print it

- too much cynicism, but information about Moscow nightlife is very good, professional and Reviewesh. One can find it at many night clubs - or have a look at
www.exile.ru site.
Rubles - yes, now rubles are OK. If the price is stated in USD - make sure if USD are accepted and/or make sure what it means in roubles, as exchange rate could be surprising, and not in your favor, of course (announcing 30 RUB/USD instead of 26 is a regular thing).
Note, that often it is not easy to get through to a really good individual girl - she may be quite busy, or unwilling to take new clients, especially not speaking Russian, so be ready it could take you 1-2 days to come to an agreement, and always keep 2-3-4 variants in reserve. And, if agreement is reached, better not to cancel it - as there could be no second try (she will just blacklist your phone No).