Mobile operator O2 has been replaced by Orange as national roaming partner for the 3 network.
The deal, which is worth a large but undisclosed amount of money, provides the smallest phone network in the UK with a back-up GSM service for customers who stray outside its 3G coverage.
Describing the deal as "fantastic", Stuart Jackson, Orange’s head of media relations, told ZDNet UK that his network was looking forward to a "significant and profitable revenue stream".
3 said on Wednesday that "Orange tendered the most competitive bid for the supply of voice, text and data services".
"The agreement takes us a good way forward," a spokesperson for 3 told ZDNet UK. "The other networks roll out new sites, and this ensures that our customers have exactly the same voice and text coverage as on any other network."
The 3 spokesperson was keen to point out that 3 would continue to increase its own coverage across the UK.
O2 hinted that Orange may have tempted 3 with a very affordable offer which it was unable to match. O2 spokesperson Simon Gordon said on Wednesday that the network was keen to win new business "but not at any price".
Gordon added that O2 would "happily work with 3 and Orange to ensure a smooth transition". 3 is promising that the transition, which will begin at the end of this year, will not result in disruption to its customers.
Reports suggested that the original 2003 deal between 3 and O2 was worth as much as £100m, but the continued rollout of 3’s own network means the deal with Orange is probably significantly smaller.