[mdasen]

I think there are two forms of interoperability that you aren't breaking out.

1. Client to Service

2. Service to Service

With email, service to service is generally free. However, Client to Service (eg. IMAP) hasn't been guaranteed to be free in the same way. Many services offer it today for free, but that's after a sharp decline in desktop mail clients. I remember how hard it was to get free IMAP back in the day. Now that most people use webmail or the company's app, they're offering it without being worried about the few people using it. If 90% of people started using IMAP and bypassing Google/Yahoo/Microsoft's ads, we might see IMAP return to being a paid service.

> AIM was free

AIM was constantly trying to break third party clients. Pidgin was often good at keeping on top of changes AOL was making to break them, but AIM certainly wasn't an open network for third parties.

MSN Messenger originally included access to AIM, but AOL blocked them. I don't think MSN Messenger (and later Windows Live Messenger) ever welcomed third party clients. Microsoft tried various strategies to get MSN Messenger to take off, but none were really open. It's more that the MSNP protocol was relatively easy to reverse engineer and Microsoft didn't go overboard trying to block third parties.

I agree with you that companies are trying to make the world a worse place via barriers to communication so they can make money. However, we didn't have great interoperability in the past. Email was interoperable, but instant messengers weren't. Pidgin was just good at staying on top of things back then and was facing off against less competent foes. If AOL were more competent, they would have been better at keeping Pidgin off their network.