There are many reasons why Twitter is a powerful networking tool, but it lacks three-dimensionality. Twittering enables you to write what you need to write in 140 characters or less, but it restricts you from adding inflection and tone.
Suppose you want to leave a voicemail message for marketing professional Stacy Crosby but don’t want to trade physical phone numbers. You know her Twitter name is @StacyCrosby so you enter her name as the recipient, click the green button to send a voicemail, and Pockets calls your previously-entered phone number. You answer your phone, press 1 to accept, and leave her a message. Then, you hang up the phone and @pocketsapp sends her a tweet, references your Twitter name, and provides her a link–where she can log into Pockets and listen to the message. If she wants to return a call, she reciprocally signs in.
For those times you don’t want to exchange in back-and-forth tweets or direct messages because syllabic inflection is not understood, call each other. Sure, you can engage in a real phone conversation or talk on Skype–but when timeliness is unimportant, this is an easy alternative.
Pockets only works for US-based phone numbers, currently.