Not a lot of people know this, but my daughter is not my biological daughter. Her mother and I got together and had a son (now 10). She was an added bonus to the relationship. She was about 2 years old when she started calling me dad and has ever since. (She's 13 now.)

She has never met her biological father, but has talked to him on the phone. The conversations started when she was around 10 and at first they were done in her therapists office as a conference call.
Initially, she wanted to know more about him and all that, but when they would talk (and it was only when it was convenient for him) he really wouldn't share anything about himself or his life. She grew tired of that very quickly and doesn't talk to him more than a couple times a year now.

We've had a few conversations about her bio-dad and it's all been pretty positive. She has lashed out at me a few times and said "you're not my real dad." But it's rare. It hurts, but at the same time, I know she's just trying to upset me, so the best way to defuse the situation is not to yell back. For being a teenager, I think she's pretty good about the whole thing and is pretty thoughtful about it.

All-in-all, she has a good relationship with her mom and I.