I'm commenting on functionality rather than quality issues, but doesn't that Podcastudio kit already incorporate a small mixer for the microphone that has additional input channels? Can you not run the audio from your phone return line(s) into those?

yes but how to connect iphone 4 with this i can use phone to receive call but problem is i have to hold phone in my hand when i receive call cos it use phones mic to talk i wan to use main mic not phone mic how is that possible ?

I would seriously suggest that you look at something like a hands-free car kit and position the actual iPhone as far away from any of the audio equipment as possible. If you have it anywhere near, your audio will be ruined by breakthrough from the phone transmission, especially as the particular audio equipment you are using is not known for its rejection properties.

Once you have the hands-free kit, you can cut into the earpiece cable and take a feed to a mixer input. Clip the hands-free mic to a boom attached the headphones you are using for the radio station local monitoring. Continue to use the podcasting mic as normal for the radio station, but your contact on the phone hears your voice through the hands-free mic.

I have a gentner microtel that's from the mid 90's but works very well with a landline style telephone. In fact, it doesn't need to be a landline (I use it on IP phones) but it must be connected to a telephone with a handset. You connect a dynamic mic to it and pickup the receiver while wearing headphones and start recording. works very well.