How Does LV Communicate with Snape?

[gelite67]

No: HPFGUIDX 148355

I've been wondering how LV communicates with Snape at HW.  

We've seen numerous methods of communication - owls, patronuses, heads-
in-the-fireplace, pictures that hang in more than one place, Protean 
coins.  (What else?) I'm assuming that the heightened security for HW 
in HBP included the same security that we saw in OOP(and more).  If so, 
I don't see how LV could have communicated by owl or the fireplaces.  
Or by pictures for that matter.  Nor do I see how LV's or a DE's 
patronus could penetrate HW (even if it could, how does a Patronus 
communicate???). The Protean coins seem to have limited communicative 
effect; they seem to act more as a signal that anything substantive. 

So how would LV communicate some urgent, substantive message to Snape?  
Is there anything in canon to support that the Dark Mark can be used to 
transmit holographic messages?  Would the security measures also limit 
Snape's ability to send contact LV?

I'm also wondering if the WW has methods of communication to which we 
have not yet been introduced.  Parchment that Apparates, perhaps?
I've always been curious as to the WW's equivalent of a telephone, 
something that would allow instant, two-way communication (other than 
the fireplace, which seems so awkward to me). 

Ideas anyone?

Angie