Breakdown of keitaidenwagaisha ni denwasuru.

Questions & Answers about keitaidenwagaisha ni denwasuru.
It is pronounced けいたいでんわがいしゃ.
It breaks down like this:
- 携帯電話(けいたいでんわ) = mobile phone / cell phone
- 会社(かいしゃ) = company
So 携帯電話会社 literally means mobile-phone company, and in natural English it usually means a cell phone carrier or mobile service provider.
With 電話する, the particle に marks the person or organization you are calling.
So:
- 携帯電話会社に電話する = call the mobile phone company
This is different from English, where we just say call the company with no extra word. In Japanese, に shows the target of the call.
More examples:
- 友だちに電話する = call a friend
- 病院に電話する = call the hospital