Apple Inc. (NASDAQ:AAPL) shares continued rising in premarket trading after Carl Icahn’s tweet about his stake on Tuesday. He tweeted that he had taken a large stake in Apple and spoken with Chief Executive Officer Tim Cook about increasing the company’s share buyback plan. Early this morning Icahn spoke with Reuters via phone, providing a little bit more information about his suggestion for Apple.

Apple - Carl Icahn

Icahn’s plans for Apple

This morning Edwin Chan and Jennifer Ablan of Reuters report that he told the media company Apple Inc. (NASDAQ:AAPL) could buy back $150 billion in shares right now by borrowing funds at a 3 percent interest rate. According to Bloomberg and Reuters, Icahn’s stake is worth about $1 billion right now, and in his tweets on Tuesday, he indicated that he believes Apple Inc. (NASDAQ:AAPL) shares are “extremely undervalued.” In fact, he believes the stock is worth over $600 per share.

“If Apple does this now and earnings increase at only 10 percent, the stock—even keeping the same multiple currently—should trade at $700 a share,” Icahn told the media company. He also said that right now the company has “huge borrowing power, little relative debt and trades at a low multiple.”

Icahn not the only thing driving Apple shares

Barclays analysts Ben A. Reitzes, Ryan Jones and Matthew Markezin-Press note that while Icahn’s tweet about Apple Inc. (NASDAQ:AAPL) did provide an immediate catalyst on Tuesday, it isn’t the only thing pushing shares upward. They have maintained their Overweight rating and $525 per share price target for Apple Inc. (NASDAQ:AAPL).

The analysts note that the company beat June quarter estimates, posting a 20 percent increase in sales of the iPhone, which they view as the company’s most important product. They also said that Apple Inc. (NASDAQ:AAPL) bought back about three times more shares than they expected it to in the June quarter. That amounted to more than $16 billion worth of shares, which they believe shows “it was already leaning in a shareholder friendly direction with a faster pace of buybacks.”

In addition, they believe new plans from U.S. carriers like T-Mobile’s JUMP! Plan, AT&T Inc. (NYSE:T)’s Next plan and Verizon Communications Inc (NYSE:VZ)’s Edge plan are not just amortizing costs for early upgrades. They think they’re also keeping Apple’s subsidy model safe for “a bit longer” while also boosting sales.

And of course like other analysts, Barclays believes investors are looking forward to the launch of the next iPhone model, which is expected next month and should help Apple Inc. (NASDAQ:AAPL)’s holiday season sales.

Apple could increase its share buyback like Icahn wants

They believe Apple could increase its share buyback even further, just as Icahn wants. The company’s current program is $60 billion, and the Barclays analysts note that Apple Inc. (NASDAQ:AAPL) has about $147 billion in gross cash right now. Of that cash, about $41 billion of it is in the U.S., while the rest is overseas.

The analysts estimate that the company’s free cash flow per share will be around $46.85 per share this year, $45.66 next year and $49.39 for Apple Inc. (NASDAQ:AAPL)’s 2015 fiscal year. They believe “Apple may need to be creative if it were to really benefit shares materially with incremental buybacks.” They used the example of a 25 percent increase to Apple Inc. (NASDAQ:AAPL)’s current plan, which would add at least $1.10 per share to their 2015 earnings per share estimate. A 50 percent increase could add more than $2 per share.