When you have a conversation in person you provide three communication cues: Words, tone, and body language. When you have a conversation on the phone you provide two communication cues: Words and tone. When you have a conversation in writing you provide a single communication cue: Words.
The common element is the word. In fact when someone describes your conversation they will, either consciously or unconsciously, convert you body language and tone into words. Your words are very important, body language and tone can only negate or emphasize them.
Think about the words you use. No matter who you are talking to, no matter how well they know you, your words are going to provide the basis of your message. Don't assume that they know what you mean. They can't read your mind.
Make sure you what you mean IS what you say.