L M Ericsson Telefon AB has decided to put much of its mobile telephone and mobile radio communications business into a joint venture with General Electric Co. The Ericsson units included in the joint venture are those in Richardson, Texas, and in Montreal that are involved in cellular telephone systems and mobile communications. Swedish units included are the parts of Ericsson Radio Systems that work in land mobile radio and mobile data and mobile telephones. Also included are sales companies in Sweden, Norway, Denmark, Finland and Spain, which together have 2,200 employees who will continue to work within their respective units. General Electric units included in the joint venture employ 2,300 people and produce mobile radio and cellular telephone equipment in the US and Canada. The employees, mostly based in Lynchburg, Virginia will continue to work for their resp ective units. GE will con tinue distribution in the US through a majority owned company, the partners said. No further details were available, but the move is a recognition of the fact that Ericsson is still do ing too much for a company of its size, and despite its successes does not have the resources to go it al one in all its activities.