Fring 3.20 (Symbian 9) was released yesterday and should fix some volume problems.
I am now using Fring for about a month on a Nokia E61. It allows you Instant Messaging and Voice over IP with Skype, Google Talk, MSN and SIP based VoIP. You can use GPRS, UMTS or WLAN (IEEE 802.11b/g) to connect.
I tested Fringe with chat to multiple partners and did not find any problems, you can easily switch from one conversation to the other using the smartphones little joystick.