I found the problem was fixed by the Fairphone software upgrade (I
discovered the Issue in South East Asia and am currently visiting the
Netherlands with a SIM working in my only useable slot - slot 2). My
phone is at Fairphone OS 1.4.2 level.
I am unsure from what you say whether you have a working SIM in slot 1
as well as slot 2, if so this may be a new problem, when I was in Asia I
disabled the SIM in settings and used Wi-Fi when available, if you do
need to upgrade than you should be able to install it this way while you
are travelling.
I have to say in my case support have been totally useless, I have not
even had the courtesy of an acknowledgement despite sending three emails
to them since February. I notice that some others have had a responses,
which seem to have been totally unhelpful.
Allan