How a number with +90 is written
International format: +90 5XX XXX XX XX
National format: 05XX XXX XX XX
Inside Turkey a number starts with the trunk prefix 0; drop it after +90.
Mobile number length: 10 digits after +90
Calling a Turkey number from abroad
From another country, dial + (or your exit code: 00 in most of the world, 011 from North America), then 90, then the national number without its trunk prefix.