This is an unusual type of collaboration. It is hard to share infrastructure and at the same time compete. I have a suspicion that this is the first stage of an integration or even a merge (?)...
Vodafone and 02 to share networks
Mobile phone firms Vodafone and 02 parent Telefonica are to pool their network infrastructures in the UK and three other European countries.
The move will save both firms many millions of pounds in operating costs, and Telefonica admitted "the current economic situation was a catalyst".
Read the whole article at: http://news.bbc.co.uk/1/hi/business/7959133.stm