When we set up Airsource, we set it up as a BREW consultancy. We rapidly sold a number of BREW projects, and built on the expertise we had acquired while at QUALCOMM. In the process, however, we inevitably found ourselves working on other software platforms, particularly on Series 60, which now accounts for about half of Airsource's work. Series 60 and BREW are often held up as competitors, though in practice I would argue quite strongly that they target very different markets.
A BREW phone, such as the Motorola V3M has a primary display is 176x220, it has 23MB of memory, and a processor clocked at perhaps 40MHz. A Nokia E65 costs nearly twice as much, has twice as many pixels, can store five times as much, and runs fives times faster. Pundits will immediately point out that the V3M is a pretty slow example of a BREW phone. That's certainly true, but the V3 series accounts for a very significant fraction of the US market for BREW phones. The Nokia E65 is similarly chosen for comparison as an example of a popular Series 60 v3 phone.
Comparing the two is pointless. The BREW phone is clearly a much lighter-weight platform, targetted primarily at games. The Symbian phone has considerably more memory, more storage, faster CPU, and generally faster network data transfer. It is also significantly harder to program for - in the same way that coding for a Windows XP PC requires rather more knowledge than writing a program in BBC BASIC did. A Symbian phone is simply more capable than a BREW one, and consequently the APIs are richer, and the learning curve steeper.
That's not to say that that Airsource's clients do not want to target their application at both BREW and at Symbian. They absolutely do. But the Symbian application will always have more functionality and tighter device integration than the BREW application, in the same way that a dedicated BREW application will have more functionality and tighter device integration than a web-based application. Clients come to us because they want to get the most out of the phone, and to do things that are non-trivial, whether that be linking into the messaging menu of a Symbian phone, porting a multi-process application to BREW, or simply writing an application that Just Works.
What this means is that while the mobile market is certainly split into markets that may not directly compete with every other platform, they form an overlapping whole that represents the mobile space. Companies want to get their application "on mobile", and by that, they mean on the maximum number of phones, with users who will spend money, for as little cost as possible. Choice of platform, like Symbian, or BREW, is therefore just a business decision, not a technical one.