Does radio use virtual photons? In radio communication each accelerated electron in the transmitter antenna interacts with an electron in the receiver antenna by exchanging a photon.
Is that photon always a virtual photon as described in the diagram below rather than a "real" photon?

As I understand it, Feynman's definition of a virtual photon in his book QED is any exchanged photon that does not appear in the initial or final conditions. Therefore by his definition radio works by using virtual photons.
 A: This is a perceptive question.  Consider the following from the Wikipedia article "Virtual Particle":

As a consequence of quantum mechanical uncertainty, any object or
  process that exists for a limited time or in a limited volume cannot
  have a precisely defined energy or momentum. This is the reason that
  virtual particles — which exist only temporarily as they are exchanged
  between ordinary particles — do not necessarily obey the mass-shell
  relation. However, the longer a virtual particle exists, the more
  closely it adheres to the mass-shell relation. A "virtual" particle
  that exists for an arbitrarily long time is simply an ordinary
  particle.
However, all particles have a finite lifetime, as they are created and
  eventually destroyed by some processes. As such, there is no absolute
  distinction between "real" and "virtual" particles. In practice, the
  lifetime of "ordinary" particles is far longer than the lifetime of
  the virtual particles that contribute to processes in particle
  physics, and as such the distinction is useful to make.

Also, consider this from the Wikipedia article "Near and far field":

In the quantum view of electromagnetic interactions, far-field effects
  are manifestations of real photons, whereas near-field effects are due
  to a mixture of real and virtual photons. Virtual photons composing
  near-field fluctuations and signals, have effects that are of far
  shorter range than those of real photons.

A: The question here really is: "When are photons not virtual?". As explained in this article:

A virtual particle is one that has borrowed energy from the vacuum, briefly shimmering into existence literally from nothing. Virtual particles must pay back the borrowed energy quickly, popping out of existence on a time scale set by Werner Heisenberg's uncertainty principle.

So to answer your question- a photon exchanged over long ranges is outside of the scale of the uncertainty principle so the photon exchanged between the two electrons is real. Also see:
http://en.wikipedia.org/wiki/Virtual_particle#Actual_and_virtual_particles_compared
A: Radio and the like are best described quantum mechanically in terms of coherent states of the electromagnetic field. These states don't have a definite "number of photons", but are rather like an infinite mush of harmonic oscillator states that behave the most like classical electromagnetism.
