We have done them both: The small, low budget expedition with 3 sherpas and a simple approach, as well as the large-scale adventure with high end technology and 5000 meters/16000 ft of rope.
Both have their charm and you have to decide for yourself which level you want to go for. The technical stuff changes dramatically over time and we will just give you a brief idea of the possibilities.
Well, you need a camera (for summit pictures). The environment is very forgiving, and even with just a cheap pocket style camera you will get some really nice shots. Bring at least 15-20 rolls of film and spare batteries. Keep your camera inside your down suit when going high.
Talk with the trekking agency or other expedition members about walkie-talkies. The yellow Motorola "Talk-about" has worked well for instance. Try to join in on a base station and share the costs.
The Nepal government will charge $ 50 for an individual walkie-talkie permit and around $ 200 for a base station. Your trekking agency will take care of the permits for you. You will then probably be assigned specific frequencies to use and will need to calibrate the radios. When in BC, you should talk to other teams about an emergency channel.
Sat-phone. If you don't bring one yourself, there will be several expeditions willing to let you buy in on theirs. They will charge about US 10-20 a minute. This is more than the actual cost (about US 4), but bear in mind that they have to cover hardware costs as well as permit costs. For a full list of sat phone options, costs and such, check the HumanEdgeTech part on this website (coming soon). Please notify us if you find new systems and gadgets that could be useful.
If you use other people's sat-phones, please don't overuse.