Both networks also spent heavily on their launches, despite the downturn in their sector. O2 is reported to have burnt over £300,000 on the glitzy PR-led launch party, and while T-mobile is remaining coy about its own launch budget, top notch global sports stars do not come cheap.
Instead of simply seeking a cuddlier, more inclusive image and trendier logo, there were hard-headed commercial reasons for ditching both old brands. Deutsche Telekom's One2One adopts the T-Mobile brand used across the firm's global mobile services. BT Cellnet owner mmO2 adopted a similar strategy, wanting to unify mobile operations in the UK, Germany, Ireland and the Netherlands.
And judging by their respective core messages - T-Mobile's 'Get More' and O2's 'See What You Can Do' - both were as keen to avoid association with phones as they were with cosmetic change.
O2 vice-president of marketing Will Harris could likewise have spoken for his rival when he stressed: 'We did not want to be seen as a mobile network, but as a services brand'.
Both held high-profile launches with a sporting theme. O2's London Eye reception was accompanied by soccer stars and boy band Blue.
T-Mobile brought Atomic Kitten together with Gary Lineker and Peter Shilton for a penalty shoot-out to promote a new handset game.
Both networks have avoided the stress on voice services, and for sound reasons. Mobile Choice editor Huw Morgan says all mobile companies are chasing ARPU - average revenue per user. To get more of it they must capture more of the lucrative contract market rather than pre-paid and persuade users to take up games, multimedia services and Personal Digital Assistant (PDA) Units.
Morgan says there is a sense within the industry that, in the past, networks have concentrated too much of their PR resource on technology - over users' heads - rather than services. Both companies, he says, want to set that right while, at the same time, tuning their brands for the autumn arrival of Hutchinson 3G's network, with its potential for increases in applications.
For T-Mobile - whose ancestor One2One had tended to be seen as the bargain end of the market - this meant a twin-track PR strategy focusing on corporate and consumer users, targeting broadsheets such as The Daily Telegraph with supplement content. O2, meanwhile, hoped to use PR to ditch BT Cellnet's 'staid' image and create a warmer brand.
Speaking for themselves, the firms put it rather differently. Spokesmen for O2, which used Edelman PR Worldwide for its domestic launch and Jackie Cooper for Europe, said the key message was 'five companies (including portal Genie) coming together' and that products from other countries would be adopted and economies of scale would accrue, leading to better deals for customers.
T-Mobile director of corporate comms Neil Lovell says his company's message is that working practices and company culture alike will be changed as a result of a rebrand: 'Now when people go to Paris they will see coverage of the T-Mobile brand. It'll be clearer that we're the world's third biggest mobile services company.'
Lovell adds that internal comms has played a significant role in the strategy and that months before the change the One2One comms department was restructured so as to launch the process of relationship-building with journalists that later accompanied the launch.
Early feedback from Morgan indicates Lovell may have been successful.
Morgan says One2One 'didn't do media relations well in the past' but said this was rapidly improving with a new hands-on approach.
And what of bigger successes? Much will depend on respective forthcoming product launches. These include what one industry source terms O2's 'killer product' - the Xda PDA - and T-Mobile's picture services via the Eriksson T-68 handset.
Lovell says customer perception-tracking has already started and would be analysed further.
Edelman associate director Neal Fullman says sensing whether 'a clear, pervasive and ubiquitous brand' had been created was a long-term project.
Jackie Cooper founder Robert Philips is more forthright, saying the agency was happy to be judged according to a client's bottom-line growth.
One suspects that when the talking moves to the boardroom, T-Mobile and O2 directors will share that singular benchmark of success.