Spirits can communicate with people aside from mediums in many ways.
They can do this by using numbers, sequences of letters, dreams, etc.
Then there are the more obvious methods such as by pendulum or Quiji.
Keep in mind though: There are natural born mediums, yes. But anyone can open the third eye with a LOT of time, patience and essentially a lot of pain. Its not all its cracked up to be, but its worth it in the end.
If you have any questions about mediumship or just want to chat feel free to send me a message.
Blessed be xx