With Sunday's non-waiver Trade Deadline rapidly approaching, general managers' phones are undoubtedly busy.

At least half of Major League Baseball's 30 teams should be considered in contention for a postseason berth, meaning at least that many are in position to be buyers. That could make for an interesting and active week.

But not every team's situation is identical. Some have deeper farm systems that can provide more bargaining chips than others, while some won't want to part with certain prospects to make a run this year. Many teams deemed "sellers" of big-league talent will be looking for Minor Leaguers at the upper levels, ones who can make impacts in the near future, offering a more immediate return on trade investments.

On the other hand, there aren't that many prospects of that ilk, so GMs will surely be asking about high-ceiling prospects at lower levels, though some of them might be fairly untouchable.

Trade Include

By now, the Major League parts on the market -- the Carlos Beltrans, Heath Bells and Hiroki Kurodas of the world -- have largely been identified. Knowing which prospects will change hands ahead of the Deadline is, in many ways, a fool's errand, but there are certain names that come up constantly in conversation. Some are untouchable, but as Mahatma Gandhi once said -- and he probably was referring to the Trade Deadline -- "If you don't ask, you don't get."

With those stirring words ringing in the ears, here are the biggest prospects, the Minor Leaguers that GMs should be asking about.

Arizona Diamondbacks: The D-backs may belong in the surprise group with Cleveland and Pittsburgh, but rest assured they are doing due diligence in terms of working the phones. With the exception of slugging first baseman Paul Goldschmidt, most inquiries have involved their pitching depth, with Tyler Skaggs, Jarrod Parker, Patrick Corbin and David Holmberg leading the way. All but one -- Parker -- is of the left-handed variety.

Atlanta Braves: If they're going to trade, it's likely to be from their strength: pitching. Exciting youngsters Randall Delgado and Arodys Vizcaino are both in Double-A. Delgado is 21, Vizcaino is 20.

Boston Red Sox: The Sox don't have a ton of elite talent now -- only Jose Iglesias is on MLB.com's Top 50 prospects list -- though Anthony Ranaudo is proving to be worthy of consideration. That doesn't mean Boston doesn't have trading chips, with teams asking about that pair, along with lefty Felix Doubront and Futures Gamer Will Middlebrooks at third base.

Chicago White Sox: They're under .500 but still within spitting distance of the top of the AL Central. That leaves them a bit in limbo, with most rumors having to do with deals of big leaguers for big leaguers. Prospect-wise, Dayan Viciedo is their top guy.

Cincinnati Reds: The Reds have one of the bigger "stuck" prospects in Yonder Alonso, a first baseman who is just about big-league ready offensively but plays the same position as 2010 National League MVP Joey Votto. They also have some catching depth, with both Devin Mesoraco and Yasmani Grandal coming fast.

Cleveland Indians: The players the Indians get the most calls about have gotten a taste of the big leagues this year: Alex White, Lonnie Chisenhall and the most recent callup, Jason Kipnis. Add in top left-handed prospect Drew Pomeranz and there's a quartet of young, talented players with whom Cleveland is highly unlikely to part. The Indians, while in contention, are a team that may not be eager to blow up things on the farm for a quick fix.

Detroit Tigers: They acquired Wilson Betemit without raiding the coffers too much, but they're probably getting asked an awful lot about right-hander Jacob Turner, who has to be as close to untouchable as they come. A pair of southpaws, Andy Oliver and Casey Crosby, might be getting some attention, too.

Los Angeles Angels: They haven't shied away from making big trades in the past, but it sounds less likely to happen this time around. The Angels traded several prospects to get Dan Haren from Arizona last year and outside of the untouchable Mike Trout, they might not have the upper-level ammunition to get a big deal like that done this time around. A Double-A pitcher like Garrett Richards could get some interest.

Milwaukee Brewers: While last year's offseason trades took away some of the "big-name" prospects from their system, that doesn't mean the Brewers haven't been talking turkey. A guy like Wily Peralta, who has a 1.00 ERA in July and was clocked up to 98 mph in his last start in Double-A, is generating plenty of interest. So is Futures Gamer Tyler Thornburg. Bat-wise, recently promoted (to Double-A) Khris Davis, first baseman Hunter Morris and second baseman Scooter Gennett have all been watched closely by interested teams.

New York Yankees: It's the usual suspects with the Yankees, with everyone still interested in Jesus Montero's bat. He's not alone, though, with the Yankees getting inquiries on fellow catcher Austin Romine, lefty Manny Banuelos and right-hander Dellin Betances as well.

Philadelphia Phillies: They've certainly made big trade splashes in the past, but they don't have much in the upper levels. They do, however, have some very good arms, particularly with Class A Advanced Clearwater. Teams are bound to ask about Jarred Cosart, Brody Colvin or Trevor May.

Pittsburgh Pirates: Like the Indians, don't look for the Pirates to blow apart everything they've built just for this run, meaning a guy like Jameson Taillon is off the table. They have heard from teams about other arms like Brad Lincoln, Jeff Locke, Bryan Morris and Justin Wilson. Any conversations about hitters likely start with Futures Gamer Starling Marte, but also include infielders Matt Hague and Jordy Mercer.

St. Louis Cardinals: Conversations with St. Louis largely go like this: "We'd like Shelby Miller or Carlos Martinez." Cardinals reply: "Click." Their two top-notch pitching prospects aren't going anywhere.

San Francisco Giants: Most conversations with the Giants seem to involve two prospects just down the road with Class A Advanced San Jose. Anyone looking for young pitching will ask about Zack Wheeler. A team that covets a bat with top-of-the-order speed will quickly bring up outfielder Gary Brown.

Texas Rangers: There's little question that everyone asks about lefty Martin Perez's availability, but it's hard to imagine him going anywhere. A southpaw like Robert Erlin could be available, as could outfielder Engel Beltre or third baseman Tommy Mendonca. Joe Wieland, a right-hander, has gotten a good amount of attention as well.