Why don't I have alerts when I plug in my handsfree headphones?

Brand new iPhone, I want to know if this is a bug or a ...feature.

I plug in my headset, and keep it plugged in all day, because I don't want to have to put the phone up to my ear. Therefore, I use the original apple headphones, as a handsfree.

I keep it on my desk. I get call alerts, I can hear them fine. I do not get sms alerts, viber alerts, or any other type of alert except phone and alarms, when headset is plugged in. I only get vibration. This causes me to miss a lot of messages at the time they're sent.

Any way to get around this...? It's irrational for the phone's alerts to shut down just because you wanna have your handsfree plugged in and not plug it in every time you want to talk on the phone.

Thanks in advance,

Katt