Concerning the standard communications, e.g. between Sandpoint and Magnimar, do we have any official information in the sourcebooks?
For the teleportation I remember James said the following (and I definitely like this level of magic for the world).
The communication is also a crucial aspect we have to define for the world in order to keep a realistic feeling.
Could we suppose the use of crows or something similar?
The elves have a network of fixed-location portals called elfgates that they can use to quickly move from location to location, but that's not the same as teleportation from the 5th level spell.
While Golarion's "level cap" (if indeed it has one, which it doesn't really) is more or less at 20th level, it's actually relatively rare to see characters of 9th level or higher. They certainly exist, but don't confuse the fact that for adventures and supplements things skew toward higher level stuff that that means they're super commonplace.
In Golarion, teleporting is not common. Even at its lowest level, getting a teleport spell from a wizard will cost you 450 gp... one way. Most wizards, i suspect, will try to charge you 900 gp since they'll probably need to cast the spell at least twice, since they have to go back where they came from. And that only gets a couple of people teleported. Shipping a huge number of people or goods via teleportation probably needs the more powerful teleportation circle spell, which runs 2,530 gp to cast.
Compare those prices to, say, the price of a ship's passage for 100 miles—ten gold pieces.
Teleporation in Golarion is for the very rich and powerful, and as such is not all that common at all. Which is by design, because having ships and long shipping routes they sail on supports a LOT of really cool plotlines, after all!
Also: Teleportation is a crazy impressive magical stunt. If it were common, it would become dull and ordinary, and that's not the type of world we want Golarion to be.