On a basic level, it is appropriate to acknowledge and show appreciation for kindnesses which are extended to you. How one expresses thanks is secondary. The more meaningful aspect is to convey gratitude in a way that makes it all about the giver.
Appreciation should be communicated in a timely manner. Whether one makes a call, sends an email, or jots a note is immaterial. The message is key. Be sure that your comments acknowledge the giver’s thoughtfulness and efforts. Tell him or her how much the gift or gesture means to you. The end product of all this is to maximize the contentment of the giver and, by doing so, to fortify the relationship between the parties.
Giving is so much more about relationships than it is about gifts or gestures. For those who wish to cultivate strong relationships, substance is always more important than style.
Remember a thank you in any form is always best. Its value goes far beyond the exchange which prompts it. Mark Twain once said, “Kindness is the language which the deaf can hear and the blind can see.” Such a treasure must always be acknowledged.