Thanks to the efforts of Reginald Barclay I know Voyager and Starfleet Command were able to communicate with some regularity. Was it ever established how often Voyager was able to communicate with the Alpha Quadrant after Barclay's first successful contact.
I thought it was once a month at first? I seem to recall in LifeLine that there is a line where Captain Janeway says in a briefing that "This is all we have from Starfleet, until next month."
At first it was once a month. However, after the events of "Inside Man," I believe they could communicate with the Alpha Quadrant whenever they wanted.
I don't think it reached the point where they could communicate at will but they were obviously honing their technique, getting better and better at it. This makes perfect sense, really. Once Barclay proved the concept, many more scientists and engineers would have jumped in and helped advance it.
The midas array bounced their messages off something stellar and unlikely which allowed for the homeland and Voyager to send a huge data packet each way once a month, however as of author author, y'know, spitting distance from the end of the whole dang shebang... A vicious cutthroat blackmarket on Voyager came into effect as people killed and offered sexual favours to collect on as many of those three minute chits as possible as a means to an end of ultimate power below decks on Voyager! (Kidding?) Kim is such a baby. Seven and Tom both just gave away their chits because the oldest ensign in the world needed to talk to his Mommy more. it's like the the writers were still penning Wesley when they put words in Garrets mouth.