As someone who has climbed the world round, it is important to find out what means of communication the area you are in use first. If you don't want to research much, sat phones and SPOT are awesome. For instance, in many parts of the Alaska Range, rangers monitor family radio transmissions and broadcast weather updates on their channel. Those little radios have gotten pretty good range over the years and are used to coordinate rescues all over Denali, Mt. Forker and Huntington. There is also line of sight CDMA phone access in many parts of the states where GSM fails leaving the european climbers begging to use your phone from time to time. SPOT beacons are great though. There are 3 levels of message you can broadcast as you probably know. The mid-one is akin to saying "I'm in trouble, here's where I am but don't alert the authorities". If you're absolutely concerned with being able to consult a doctor or ranger at any time, get a sat phone. You don't have to depend on Globalstar either. Iridium is still functional and outside of North America, Thuraya is fantastic. I've used BGAN for data access in the deepest, darkest parts of the world but at $6/mb, you'll want to keep it to emails. I've also rented Iridium phones for use in Nepal. They are light, cheap-ish, rugged and still completely functional despite ownership changes. You can rent or own cheap handsets and buy minutes when you need them. If you have global rescue insurance through a club like the American Alpine Club (AAC), you can initiate an insured rescue call from a sat phone anywhere in the world or just call friends and family when you are lonely.

Most importantly though, don't rely on technology to get you out of a jam. Avy beacons fail, GPSs die, radios don't reach people on the other end. They are all wonderful, life saving tools but odds are you won't need any of that stuff. Read the Wilderness First Responder medical book, read Freedom of the Hills, etc. Go prepared. A vast majority of the time, you'll be able to get yourself and other people help without 'calling' anyone.

I regularly travel to London and Oxford on business and have been a tourist there as well. If you have a netbook, it'll be perfect. A laptop is also fine. You'll want it for researching stuff to do on the fly. Couch-surfing, pub-crawls, restaurants, etc. Internet Cafe's with actual computers are a dying breed. Most places expect you'll have your own hardware. There is no "region code" to change on your wireless. It'll work fine. Your laptop (and most any electronic) power supply already handles the 240V 50Hz power out there. It'll say on the power supply. All you need is a plug adaptor; a very passive, cheap device. If you bring a phone, make sure it is tri or better, quad band GSM and if you plan to use your US carrier, make sure to call them and add international use (free to add, expensive to use) so they don't block your phone from logging in out there.

Be your own tourist. Some people here are telling you to go museums and what not. Tourists will tell you what bus tour is best. Forget all that. If you like to walk around town, the city is certainly walk/tubeable, even in winter. If you don't like museums much here, you won't there. If you're in to history, you'll love the place. Things like the Tower of London are a thousand years old. If you like pubs, there are some great, historical ones a tube ride away (e.g. The Hollybush pub in Hampstead). Like any metropolitan city, there is great fashion, food, arts and entertainment.

Other things to be aware of. Hotel ratings are not like they are in the states. A three star hotel out there is awful with leaky plumbing and old furniture. Some of the hostels are actually quite nice though if you bring ear plugs. Look right before stepping in to the street. If you get a chance to drive and you like it out here, it is a blast out there! Oxford and Kent aren't far. Flights on discount airlines like Ryanair are cheap if you want to hop up to Scotland or Ireland. Don't over plan or overpack.