Hi José,
Unfortunately Report-IT does not currently have a balance control like the TLF300. However, it is possible to achieve the same results using a combination of the Report-IT provided level controls together with the volume controls found on the side of the iPhone. He is an example how this can be used:
1) Ensure that the Monitor Input feature is switched on (so that your own voice can be heard through your headphones attached to the iPhone).
2) Adjust the Input slider until the desired sending level to the studio is achieved.
3) Using the buttons on the side of the iPhone, adjust the iPhone volume until you are happy with the volume level of your own voice.
4) When audio is being received from the studio, the Return Channel volume slider can be used to then boost or lower the return audio as required.
I.e. the combination of both the iPhone Volume controls and the Return Channel slider level is effectively the same as the single Balance control found on a TLF300.
It is also important to remember if you are intending to use headphones during the cross with the iPhone, you should setup the above with the headphones plugged in since the iPhone maintains separate volumes for headphones and the inbuilt Receiver/Speaker.