I also checked local law sources here (in Turkey) , seems domain registration and marketing activities are considered enough for most cases.

Possibly enough as evidence that you are using a mark, but owning and protecting it is something else.

Maybe Turkey does something peculiar, but the usual pattern of trademark laws is that if A starts using a name, logo etc. and later some troll B applies to register it as a trademark, B might succeed (no conflicting trademark is registered, and A's prior use can be ignored or considered unimportant) and force A to pay and/or cease & desist even if A came first.

That's why trademarks are usually registered far before actual usage (so that A owns the mark and B has no possibility of squatting).

Well, I didn't decide to use SimX name yet as it involves buying the domain, but if I do I'll not just rely on using first but will register it too.