@Estel
If you try to repair a circuit with soldering problems without any idea of the exact part of it that has a false contact or a desoldered pin, you can discover that very often applying a pression to some part of the board seems to solve the problem for some time. (also when the point of pressure is at many centimeters of distance from the real problem).

Then, when you discover the real (logic) point of the circuit explaining the wrong behavior, you will be able to see a little, invisible son of XXX with a soldering defect... This is a very common story...

EDIT:
take care, i have not tried to fix a phone with this issue using this information, but i think that if i had an N900 with the telephony function disabled i would try to check that transistor and if misplaced i would at least try to heat it up with an hot air desoldering station.(without move it away)
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