Up until the mid-90's, phone was king. Have your person call my person and let's do lunch. Then along came e-mail. Then everyone got sick of e-mail and how unwieldy it was, and is, for both quick and detailed communications. Those of us who still use e-mail as our primary platform for work communications are considered old fogies now.
The new king of interpersonal communication on the job is... text messaging, and the cell phone, and still e-mail, and instant messaging, and, oh yes, that plastic hunk of junk still sitting on desks (known as a phone, the kind that still actually plugs into a wall). In other words, there is no king of communication platforms.
What does this mean? As someone who wants to communicate effectively with both colleagues and clients, you not only need the people skills to do so; you also need to know each personal contact's personal preference for communication.
If you're juggling a lot of contacts, you may need to organize this information somewhere other than your head.
A little black book perhaps. Retro, but effective!
p.s. The flip side to all of this; Be clear with those contacting you how you are best reached. If you're all thumbs, for example, make it clear text messaging is the best way to reach you.