But following this model, you can offload capabilities that belongs to the conceptual client or server onto another network element entirely. Proxies are fine if they are not transparent - they must make themselves known, and they must be able to communicate their capabilities both to the server and the client. This of course takes an extra round trip, with the latency following that. The first choice must be with the client - it must be able to select which protocol to use for the request. An issue is of course to sense the network capabilities.
Latencies are the big network problem.
The third choice must be with the server - it cannot use protocols which it does not have implemented. WAP sits between the telephony and the Internet. It is important to pick the pieces from each that speeds up deployment and acceptance - not slows it down. WAP is a transaction environment - and retrieving a news telegram is an information transaction. Short message sizes and self-contained messages is a necessary feature.