| Hello 86. RT here. Welcome to the forum.
Those are excellent questions. Here's my take, based on my visits. I watch what the locals do, and pretty much follow along, occasionally throwing a few extra soles around here and there.
Peru is mostly a non-tipping culture. For the most part, the price is the price.
Taxis: Half the time, I am quoted the gringo price. I just pay it, because it is only 1 or 2 soles above what it should cost. When I am charged the 'right' price, I usually throw the guy a sol or two, depending on traffic, safety, politeness, etc. The drivers are always surprised and grateful. Taxi fares are relatively cheap, so I don't recommend worrying at all about them; just pay what they ask -- you'll probably be gringo taxed anyway.
Restaurants: All restaurants automatically include 10% in the quoted price. What the people I know do is add another 5% or so when they get your change. The restaurant will be helpful enough to give you an assortment of coins and bills when you pay to make it easy. If I am overwhelmed with the food and/or service, I tip a little more than that.
The one exception that I know of is at La Mar. At that restaurant, they post that they do not include the tip in the price, so tip like you're back home. The food is great there, so you'll be happy to fork over a few bucks.
In the cheaper places (4-8 sol lunches), they do not expect tips, but I leave a sol or two, mostly because I can afford it. One time, a girl chased me down the street, because she thought I forgot 2 soles on the table.
Casinos: The drink girls and the dealers rarely get tipped. If I have a good run, I will give the dealer a couple of dollars, and I give the drink girl a dollar every second or third drink. I have hardly ever seen a local person tip the drink girls.
Hotels: Depending on how much my adventures mess up the room and my towel needs, I will give the boy who makes up the room (they're usually male, for some reason) 10 soles if I happen to be there when the room gets made up, 20 if I'm there for more than a couple of days. They're usually grateful.
As to your phone questions, if you're staying in Miraflores, most of the people in the phone stores are used to Americans who can't speak Spanish -- and face it, there's only a couple of things that we want, and they've dealt with it before. You should be OK with just pantomiming. You might even run into an English-speaker in some of the Miraflores locations.
However, even if you have an unlocked phone, I recommend that you just buy a prepaid phone at a supermarket kiosk or phone store. I saw them for as low as 79 soles this week (~$25). If you're like me, you're busy screwing your brains out and will not be thinking straight all the time. That's a prime opportunity to lose a phone (I speak from MUCH experience on this subject), and it sucks less to lose your non-regular phone. There's two main companies -- Claro and Telephonica. They both claim to be the best and cheapest. Cell calls to the 'other' company are costly; many Peruvians have phones from both companies to avoid this problem. Just buy whatever phone you happen to come across first -- you'll be fine.
Enjoy your trip. We answer questions for a price: report back on your experiences, please. | 
