Old question but I see it linked a lot so I’m going to add some information I believe is pertinent. I received the following email from the Austrian BMI regarding entering visa-fee before a Visa D is valid. Keep in mind this is a translation from the original email in german and from an Austrian governmental agency:
“If the visa-free stay is short or the travel purpose for the visa-free stay is different from the one for the visa D stay (eg first tourism, then study/employment), the entry would be lawful. Whereby a visa-free entry (observing the rule: 90 days per period of 180 days) and the subsequent stay with a visa D is seamlessly possible.”
Suggesting that a third-country national with visa-free privileges may enter before validity date on the D Visa and that a “Visa Run” to the UK is not technically necessary
We have an extremely similar question already about switching from a C visa to a long-term D visa. The consensus is that these sort of switches are not regulated anywhere, so there’s no reason for border officials to deny you entry.
Experience from people on various forums also confirms it:
My country doesn’t need a visa to enter the EU/Switzerland, but I did need one to be a student. I took a leap of faith and came in exactly 14 days before it was valid, because I was told I need to register with the Kreisburo within 14 days. I am still not sure this is the exact number of days, but I believe it was at the time. I phoned the Swiss Embassy in my country before and they said FOR CITIZENS OF MY COUNTRY there should be no problem. I asked them for some kind of proof, article to support my claim but they didn’t have anything. I wrote down the number of the Embassy who told me this, in case I ever needed it.
My port of entry was Amsterdam. The guy looked at me and said "Your visa is not yet valid…" I said I knew. He talked to his colleague and they agreed I was allowed to enter Europe as a citizen of my country regardless of this student visa business. I honestly think they could have said no just as easily but they were probably having a good day or something.
and
I had a similar experience as avita, I arrived to CH about 4 days before the start date on my visa since the people at the Swiss consulate told me it would not be a problem since citizens of my country don’t need visas for short time stays. The Federal migrations office confirmed that. So, I arrived 4 days earlier and registered two days before the start date of my visa. The lady at the registration office didn’t bat an eyelash, everything was smooth.
Also see our related question on moving from a Residency visa to a Tourist visa, in case you will need to stay longer at the end of your visit to Portugal.
Credit:stackoverflow.com‘