skype alternatives do have a (small) chance despite strong network effects.

1/ policy makers do not like running a third-party closed-source obfuscated binary with undefined behavior aggressively evading firewalls inside their business or country (in the case of China).

2/ the network effects are not nearly as strong as, for instance, ebay's. i do not care about being able to call random strangers on skype, only about my contacts. the scope of the network effect is to some extent that of a social group, not an entire market.