Deutsche Telekom's T-Mobile and mm02, the former mobile phone division of British Telecom, last month notified the European Union competition authority of their plans to co-operate.
The companies believe they can make 30% savings through joining forces to build base stations and antennae for the high-speed mobile technology.
"The Commission concluded after looking closely at the proposed cost-sharing initiative that it would not be anti-competitive and would benefit consumers, as it will hasten the roll-out of 3G services," said Amelia Torres, spokeswoman on competition issues.
The Commission is still considering whether to allow the two companies to share radio frequencies, however.
In spring of this year a rift emerged between two of the European Commission's top officials over how to deal with the mobile phone sector, which has bben hit hard by the economic slowdown.
The European Commissioner for the information society, Erkki Liikaanen, wanted to grant the struggling firms some immunity from the tough competition rules, but his colleague Mario Monti, in charge of competition, insisted that the rules must apply "during economic downturns as well as during boom times".
Monti's spokeswoman said his position remains unchanged and denied that the commissioner has changed his tune. "Mr Monti was not opposed to such partnerships. He said he would look closely at such plans because of the relatively few number of players in the mobile phone market, and that is what he has done," Torres said.
The European Commission will probably make a final decision on the cost-sharing plans of mm02 and T-Mobile in Germany and the UK next month, after it has received comments on the plans from rival mobile phone operators in the two countries.