This app was mentioned in 3 comments, with an average of 3.33 upvotes
In my part of Russia, Uber and Gett [1] are reliable. I'd never heard of Gett before I came to Russia, but it's actually better than Uber because it has more drivers. I've never had a single problem with either one and have taken them lots of times. For sure they will both work in Moscow and St. Pete... not sure in those other two cities. But they are fine in my Siberia city of about 1M people.
Hailing taxis on the street without speaking Russian is just a recipe to get quoted absurd prices or have the driver otherwise try to take advantage of you.
If you stay in a city more than seven business days you must register your visa. (Registration is a huge pain in the ass unless your hotel does it for you, but they'll only register you for the time you are there.) If you travel so much that you don't need registration, then save your plane/bus/train tickets so you can prove you weren't anywhere more than seven days.
SIM cards with data are dirt cheap, far cheaper than the USA. You can easily get one at a shop but you will need to show your passport.
Don't drink the samogon. (Russian moonshine)
If you have dark skin you may get stopped by the police for a document check. I had a guest here from Thailand, and he got stopped twice on/near public transit in a four-day stay. But I've never been stopped once in four years.
[1] https://play.google.com/store/apps/details?id=com.gettaxi.android
Strangely, Uber shows up on Google's "Android Wear apps" page: https://play.google.com/store/apps/collection/promotion_3000cf4_android_wear_all
In the mean time, Gett/GetTaxi works with Wear's "call a car" command: https://play.google.com/store/apps/details?id=com.gettaxi.android
I would recommend a black cab (the licensed taxi) over Uber, mainly because a cab is way bigger than a usual car, no matter how luxurious it is. And I love the taxi experience in London.
Going out of a coach station, you'll probably find a big line of cabs waiting for passenger.
When I need to order one in advance, is use the app Gett which is pretty decent. Regular Black cab driver uses it to get client. You can either set a pickup in advance, or get one right away.
If you want to use it, PM me so I can give you a coupon that will give both of us £10 off the next ride!