A group of community banks is poised to fulfill a high-tech goal it set last year: to let customers buy and sell bitcoin on mobile banking apps. An estimated 300 banks, some of which unveiled their plans in June, will go live in the first or second quarter with this service with the help of the fintech NYDIG. The banks, the American Bankers Association and the Independent Community Bankers of America have made investments in the company as part of the effort. Several regulatory and security concerns have been worked out in the months since the initial announcement, and partnerships and integrations between NYDIG and the banks’ existing technology vendors have been completed, according to participants. The initiative addresses a need customers have clearly expressed, banking and trade group officials said.