We have traveled extensively with our two year old, both domestically and internationally and both when he was an infant and now that he is a toddler as well. My best advice is to call the airline directly, explain your situation and get VERBAL information on what is and what isn't allowed at the time of travel and what suggestions they have for you. I have even gone so far as to write the name of the operator down and quote them at the airport in case they decide to change the rules on you when you arrive!
Unless this policy has changed (???) it is like you said: only during take off and landing they make you take the baby out of the carrier (some airlines make you stap them into a seatbelt that hooks to your own during that time). Beyond that, I don't know. I have always seen babies in front carriers and I don't understand why they would change that. I am thinking that whatever you read must relate to a child with a paid seat and not a "lap child" that is being secured by the parent.
On one flight we requested the bulk head and a bassinet (it attaches to the bulk head and has a zippered band across the middle that keeps them from falling out, I think only available on international flights, but you should check) that our baby was able to sleep in. This is a GREAT OPTION if your flight is a long one!! They did make us take him out of it when the seat belt sign went on during turbulance, but even then our flight attendant worked with us to keep him in there as long as possible. It seemed that they were trying to make everyone as comfortable as possible. Hopefully they work with you too.
When my child was an infant I would stuff the Bjorn into my carry-on and take him in the airport in his carrier (infant car seat) set into a Baby Trend Snap-n-Go Stroller (also awesome for travel, very small and light weight). They would check in the stroller and carrier at the gate then I would get the Bjorn out. Of course this used to be free and the stroller was not counted as part of the luggage limit. I know that they are much tighter now so ask what the new policy is.
If you don't want to take the car seat you can rent one with a rental car if you are going that route, or ask the people you are visiting to borrow one or buy one at a second hand store...then you don't have to have lug the one you've got. In some cities there are also baby equipment rental businesses, so check around.
Sorry so much...we have just traveled so much and have really stream lined how we travel. Hope some of this helps.