NEW YORK (MainStreet) — There are over 20 trillion frequent flyer miles in circulation according to some counts, and that number is so immense it would dazzle even a hedge fund tycoon - but feast on the particulars. Last wek I was in Rome, flown by Delta, which accepted 150,000 SkyMiles for two tickets. Better still, I got the SkyMiles in a two for one swap of around 75,000 American Express rewards points.

Value the tickets at $1,000 apiece which in the calculus of miles redemptions counts as a win (a penny per mile is baseline, anything over 2 cents is a victory).

That incidentally is the only time I have flown Delta in the last 10 years, and I opened the SkyMiles account only to take advantage of the limited time Amex points doubling deal. That is how I scored.

As can you.

Fact: you will commonly hear that with so many miles in circulation, you cannot redeem them for anything you want, but know that in the past five years, I have been to Paris, Berlin, and now Rome, flyng on airline miles.

Then there is Brian Kelly, founder of ThePointsGuy.com who said that he recently traded in 150,000 miles to score an around the world trip, flying in business and first class. Along the way he spent five nights on the beach in Goa, India where. you guessed it, he paid in points.

"Less than 25% of us make good use of their points," Kelly added. "More than half don't understand the programs. They redeem them for the easiest things."

"The points game is a game," added Christopher Barnard, president of Points.com. "You have to play it to win."

Earning miles is easy. Of course they are awarded for actually flying, but they also can be had for using certain credit cards, for shopping at particular stores, even for sending holiday flowers via a particular florist.

Airlines love their miles programs. "They are huge moneymakers for them," said Kelly, who acknowledged that airlines are very secretive about their programs. But the reality is that the programs are known to generate customer loyalty, and that is a good thing in a business where the products long ago were commoditized. There is no real difference between a coach flight from JFK to Rome on United or American, and that is indisputable.

But a frequent flyer who covets his United or AA miles won't think twice before booking with his preferred carrier and, yes, we all belong to many rewards programs (Barnard says that on average most of us belong to 18). Yet we are all in on only a few, and it's those programs that win our business.

And in return there are sweet rewards awaiting those who play the game right, with the sweetest for most of us registering as travel.

That means many of us have a dream trip we are saving for - be it Rome or Moscow or Rio - and the blunt truth is that that travel can be ours if we play the game right.

"It makes for good press that it's impossible to use miles for flights," said Barnard. "But it's not true."

His guesstimate is that up to 10% of the seats on any flight are free.

There are enormous variables. On December 23 there may be no free seats or, if there are, they are awarded only to high ranking elite customers whose business really matters to the carrier. In the peak vacation month of July, scoring free flights to Rome may be a silly dream for many - but go to Rome in early December and getting seats is as easy as a mouseclick.

It can happen if you book early - or sometimes late. Spending miles on prime travel nine months ahead of the trip is a good way to get what you want - but, said Kelly, he often sees new reward seats opening up within five days of departure as airlines decide that probably they are not selling the seat for cash, so they might as well take miles.

"Don't give up, keep checking," said Kelly, who indicated that camping out on an airline's rewards page to maintain a check on any newly issued reward seats just is part of playing to win, especially for getting last minute and peak season seats.

Also, understand that promotions are an ever changing part of the game. Right now, for instance, American Express is sharply discounting the number of points needed for some rewards when the transactions are conducted via a mobile app. Airlines, too, often offer miles bonuses for flying to certain airports, on certain days of the week.

Is all this worth it?

You won't ask when your next trip is free.

--Written by Robert McGarvey for MainStreet