

Two things to watch for:
In Germany (and I think the same holds for Sweden) only some
of the connections can handle tone dialing, so make sure the
phone can be set to pulse dialing.
In Sweden, the '0' is the first digit and all other digits
are pushed "down" by one position; this makes dialing (and
in the process converting numbers) an interesting task.
Otherwise, it is technically no problem to connect a foreign
phone to either the German or Swedish phone system.
OTOH neither you nor I would ever try that, as it is of course
illegal.