First, you should find that the control wheel intercom selector does latch on your B737s. This is not an ideal system, but which bits of the geriatric Boeing are?
Second, there are several airlines (in the UK at least) who have recognised that intercom promotes a safer flight deck, not only in terms of pilots' hearing, but also by allowing a stress-free 'no problems catching that last remark' environment.
You're right about the defficiencies inherent in shouting across the flight deck. Sadly, you'll find that Health and Safety rules allow the noise level in the B737 - just.
The other challenge is getting around managers who think it 'sexy' and 'big' not to wear a headset properly.