The two sources said Verizon was now ready to push more aggressively. It hopes to start discussions with Vodafone soon for a friendly agreement but is prepared to take a bid public if the British company does not engage, one of the sources added.
"I don't really see this as a surprise," one of Vodafone's 15 largest investors told Reuters, on condition of anonymity. "The talk about this deal has been quite intense recently.
"They should look to return a large amount to shareholders, retaining a relatively small amount for deleveraging and bolt-on deals. I don't think shareholders would be pleased with Vodafone viewing any disposal proceeds as an acquisition war chest."
Vodafone Chief Executive Vittorio Colao has so far said he has an open mind on whether to sell the group's 45 percent stake, which has come to make up around 75 percent of the firm's value in recent years as its core European business suffered.
Some analysts believe the Italian, who has won praise for his dealmaking in almost five years at the top of the group, could try to hold on to the asset for a little longer, until he sees some sign that his core European businesses are starting to stabilize.
But Colao will also know that the U.S. market could become more competitive due to a wave of consolidation, so he could decide that it might soon be the right time to walk away.
"The tax problem has always been the issue. If a way can be found around that, then it is highly likely that a deal will be done," the top-15 investor said.
Another way to avoid the tax issue would be for the two parent groups to merge, but Verizon said earlier this month that it was not looking to buy or merge with its partner.
Verizon, which is benefiting from record low interest rates as well as its own strong stock price, is instead confident that the company can raise about $50 billion of bank financing, the sources said. It plans to pay for the rest of the deal with its own shares, they added. The sources asked not to be named because the discussions are confidential.