The only way would by using verbal communication or non-verbal, aside from writing. This can include using body language (ex: smiling, frowning, crying, etc), it can include tone of voice, it can also include behaviour such as avoidance or ignoring. Talking is most common, but sign language is also used, in addition to said.
Orally, you know talking, singing, music. Or visually through sign language, hand gestures, videos, pictures.
If both people knew Morse Code, and they had a Morse key and oscillator, they could communicate that way.
Depends in what sense, but perhaps through signals and gestures =)
I often use mental telepathy....