My iPhone 4 bluetooth is not working

My iPhone 4 bluetooth is not working. I have recently bought two iPhone 4 from a colleague. Both have bluetooth problems as mentioned below.

Here's what I did and found:

1. I turned on bluetooth on my iPhone 4

2. Then I turned on bluetooth on my nexus 7

3. Nexus 7 found my iphone 4, then I started pairing my nexus 7 with my iPhone 4.

4. Pairing successful. iPhone 4 showed Nexus 7 listed.

5. But when selected Nexus 7 in the list, within a few seconds, message popped up "Nexus 7 is not supported".

The same situation occured when I tried the above steps with my sonyerricson W580 phone.

But my Nexus 7 and sonyerricson W580 can easily communicate over bluetooth.

Can anyone suggest me what to do in order to make the bluetooth on my iPhone 4 to work?