Satellite phone and GPS to use in Mongolia

My son is travelling to Mongolia soon, and has been advised that he needs a satellite phone and GPS to use when trekking. He is spending a week in Tokyo before going to Mongolia (he is backpacking!), and wondered where is the best place to buy the kit he needs. Can anyone help? He has been told that Akihabara is a good place to look, but is there anywhere in particular? Thank you.

Amazon Japan

Are you sure you want to buy a satellite phone, or renting may be the way to go.
Do a search with the following words (or both combined), and you get a few hits.
You may need to translate as required (I have not found any English-friendly web sites on my preliminary search).

衛生携帯電話 - satellite portable phone
レンタル - rental

Oops, a typo on my previous post.
Correction: 衛星携帯電話　(satellite portable phone)

Buying means you need to have a service plan also.

As said, Amazon Japan has the sat phones available as sim free sold by Thuraya , and prepaid phones cards are available on Amazon Japan from Thuraya.

If ur son is traveling by himself then needs sat phone. Or it's organized by somebody he does not need it.

Oska