I don't think that you'd get very far with these old fashioned phones. Better use a mobile phone like most young and trendy Russians. As a tourist you can only buy a sim card if you have your passport registered in the city and for the date when you want to buy it. If you buy one in Moscow for instance, check that you get a good coverage in Siberia or have the roaming turned on if applicable.
In Russia it is customary to remove your shoes upon entering a home. Russians do not like to track dirt into their homes and often Russian streets tend to be a bit dirty.
Also, it is customary to bring small gifts when visiting.
For more information and cultural tips go to the web site link I have posted below.
Toilet paper - I found that not everyone uses what we know as toilet paper, many people use other means. You may notice a little enveleop hanging on the wall with newspapers cut up in squares, this is to take the place of TP. I recommend that you kind of crumple it up or rub them together to soften them up a bit before using.
Most of my time in Omsk was spent at apartments of family and friends. The apartments may not be pretty on the outside (this is a picture of the apartment I stayed in, in Omsk), but eveyone seems to take pride in the appearance on the inside. One commonality I saw was the hanging of persian-type rugs on the wall. This seems to add color and character to a main living room.
Bearing gifts - I recommend bringing a gift as you visit someone's apartment, even if it's a small one. Liquor, food, or something as you sit around and talk to add to the festivities is always welcome. The people I visited really seemed to try hard to make my visit a special event, no matter what situation they were in. Try to make your visit special for the hosts, just as it is special to you.
Offering Money - If it is a friend, you must be careful with how you offer money. Here is a little story of how I learned this. On my 2nd trip in Omsk a friend was driving us all over the place. After about the 3rd trip I started feeling guilty (maybe my Catholic upbringing), so I offered him money for gas. He was totally offended, like I was thinking less of him. I needed to explain it is common to offer money for gas in the US, which made the situation a little better.
A better approach would have been to go to a store or kiosk and pick up something he would have enjoyed: liquor, a special food treat, or somehting like that. Or, maybe I should have just planned to send him a little package once I got back home.
It seems a gift is a much better appraoch than offering money. I learned the hard way.