The deal will bar either company from entering into a material transaction for a year without the other company's consent, the source said, which would prevent Charter from immediately tying up with Verizon Communications (verizon.communications).
The agreement will allow the companies to cut costs and share technology expertise, the source added, asking not to be named because the matter is private.
The partnership is aimed at cutting the significant costs of entering the wireless market, as well as speeding up entry.
J.P. Morgan Chase & Co (jpyyl) analysts wrote in January that building a wireless business could cost Comcast hundreds of millions of dollars annually in the first few years, potentially cutting as much as 5 cents to 10 cents off earnings per share in 2017.
Representatives for Comcast and Charter declined to comment. A representative for Verizon could not be reached immediately for comment.
Comcast in April became the first major U.S. cable provider to enter the highly competitive wireless market, announcing a wireless service with an unlimited data plan. The service will launch in coming weeks, the source said.
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Comcast 's service will launch on Verizon's airwaves as part of a 2011 agreement between the two companies. It will allow customers to switch automatically to Comcast 's Wi-Fi hotspots from 4G LTE.
Comcast is moving into wireless as cable companies seek to add more services to reduce customer churn, or attrition, as younger viewers shun high-priced subscriptions in favor of cheaper online options.
Rival Charter has said it will introduce a mobile service in 2018.
In January, Reuters reported Verizon was interested in exploring a combination with Charter as part of a long list of acquisition targets, but no proposal had been made for a tie-up between the two companies.
Speculation over a combination of the companies underscores the pressure the nation's largest wireless carrier faces to make a deal in the wake of AT&T's (t) planned $85.4 billion takeover of Time Warner (twx), Verizon and other carriers also face a saturated smartphone market.
The Wall Street Journal first reported the partnership, without giving further details.