A little bit more information than what's found in the owner's manual. At least this tells you what you can do with Siri EyesFree (commands).
It the same button as the "off hook" phone, but you need to hold it in longer. The button the the one that is farthest to the left on the steering wheel.
I used that method to access Siri, and found Siri refused to do some things. It may have been answers to questions, but I don't exactly recall. I use Siri a lot. It does a perfect job with making phone calls, finding people in my phone book. Much better than the voice in the car. So to get around this I access Siri from my Bluetooth ear piece or push the home button on the phone.
My understanding is that you are talking to Siri on the phone. It should do everything you can do with invoking it on the phone. Why would it be any different?
Thanks for the responses. Yes, the phone is definitely connected via bluetooth. If I hold "home" button on the iPhone 6 I can see in Toyota Touch display that i'm calling "myself" and siri works via the speakers in the car. It's just that no matter how long I hold "call", "hang up" buttons on the steering wheel it doesn't trigger Siri. I've checked Siri and other settings in the iPhone but didn't find anything related that could disallow such a feature.
I assume the phone knows where the Siri request came from. When it was from the hook button on the steering wheel, it restricted what it would do. To test Siri from the car I asked what is the distance to the moon. Siri said something like it could not process my request. But call John was ok. I doesn't make a lot of sense. There must be a list of what it won't do. But I have a work around, so I'll never use it from the hook button. I have the phone Bluetooth connected to the car and my ear piece. So I can answer the phone from either one.
Did you check if it's offered in Lithuania? I don't know if it's a North American feature or a worldwide feature. But yes, you can always use the Home button. That's what I do in the Gen 3 if I need to use Siri.