Notices

Very useful ... but it doesn't work on Italian landline due to international prefix.

Italian landline gave error if you digit Italian international prefix from Italy

mobile doesn't care it ... it's quite better to have if you travel outside Italy but for landline you have to bypass it.

I could implement a filter that would remove a configurable prefix from all numbers. It's now on the list of features for the next version. I'm quite busy at the moment though, so I can't promise a release date.

I'm aware of the fact that my response is coming rather late. I've done some measurements myself and I can definitely say that the amplitude of the lowest DTMF frequency when played by the N900 speakers is much smaller than the other ones. This is a good explanation why tones using that frequency (1, 2, and 3) are not detected reliably. Please see the attached screenshot for reference (it contains the sequence of the eight DTMF frequencies from lowest to highest played by the N900 and recorded with a high quality microphone).

Given that I'm now using a Jolla as my primary device, I do not have much motivation to introduce a hardware specific change to this software unless there is still a significant demand for it ...

birefringence, it is your software, but I would be a big user of it were it able to reliably connect a call.
It is lazyness on my own part to want to fire a DTMF rather than key the number, especially long easy to futz international dialing codes, but I have to use land line phones and sometimes also radio autopatches. I was excited when I first got my (still everyday phone) N900 to see and try this plugin. I was also disappointed that it rarely worked for me considering the potential utility.

Ok, I've added some heuristic fudging of the amplitudes based on the picture above. Further recordings seem to show that the situation has improved quite significantly. It's not perfect, but DTMF has been designed to be robust against these effects, so I hope we're in the window of tolerance now and should have a much higher detection rate.

Please test. I've uploaded a new version 0.2 to extras-devel.

This did it, just tested on landline after update, thanks!

what does this thing actually do ?
how and where is it used ?

Nokiabot, it generates the touch-tone tones that when played over an open dialtone will dial over an ordinary wired telephone system.
It is also useful for hacks like a radio autopatch which turns a radio into a simplex telephone and other DTMF controlled stuff.
https://en.wikipedia.org/wiki/Dtmf

Thank you for getting back to us and fixing this.

Thanks biketool for testing! I've promoted the package to extras-testing.