It's the IrDA protocol that is half duplex - so all IrDA devices are.
If you just want to use it for Internet access then I think it will be fine. I often don't get much higher speeds out of GPRS anyway. So, unless you have a 3G phone, have paid for faster GPRS or are in an uncongested network cell then I don't think you'd see much practical difference.
The problem I always had of browsing via an IR phone was trying to balance the phone on one knee and the handheld on the other while sitting on a train
So I got a bluetooth card and phone instead.