You are fooled, if you think in categories like one phone system is more secure than another!

Here are my top concerns as disillusioned user using a phone for security sensitive stuff:
1. The (mis)-use of sudo and root to give some applications the possibility to do their intended purpose without any passwords at all, is simply a big, big security hole in the linux system.
2. While real (as in: for the PC) linux distributions do a lot of work to fix bugs and security holes, the aging libs and kernel in maemo is not maintained by nokia, maemo devs, or kernel.org at all, it is simply an old kernel. In the beginning you could get packages from Debian installed, but even getting them from some repository archive for one release before Debian Oldstable, they do not install, because the libs in Debian Pre-Oldstable were at some time maintained, and they do not anymore play nice here in Maemo.
3. The real security concept seems to be: 'Well, nobody cares for us, we are a small, a very small, target, with no real appstore, but a number of repositories, where you have to really learn a new way of contributing, if you are an application developer and a widget set, nobody else uses in the phone market'.

There is no security awareness in smartphone business, well, RIM had it for some time. There is no real encryption, the GSM protocol for data and voice is hacked since a couple of years. There is no easy setup of, even, email encryption, not dreaming about Voip, SMS, chat or a wallett. Applications to monitor the users are common practice, be it from manufacturers, providers or application developers.

To take advantage of FOSS and the concept of 'providing security by openness', there are too few developers actively contributing security fixes. I like the fact, that from day to day people here have still new features in their applications and new ideas. But security is not on anyone's agenda.