Recent changes in iOS have made most of this article superfluous. There are really only 2 options here. First is Push, where we register your account from our server when the app leaves the foreground and 'listen' for incoming calls. The other option is Standard where the app continues to be registered when the app leaves the foreground and will continue to receive calls until you close the app completely.
In this case, Push will be the best solution for almost all users. There are really only 3 options where one would not (or could not) use them and would use Standard instead.
1. Your SIP provider restricts where you can register from.
Our servers that register your account for Push Notifications are in the US. So if for example your SIP provider is in France and only allows registrations from France, Push would not work for you. But this is rare, most providers allow you to register from anywhere even if there main userbase is in one country. And if you do have a provider with a restriction like this, you can have them contact us. If they are willing to whitelist the IPs for our servers that handle Push (there are only a few), then that should get Push workiing for them.
2. You have a PBX that is only reachable from the local network.
Our servers are obviously not within your local network :) , so if your SIP server is only reachable locally, then Push would not work for you.
3. You have some special security needs.
For Push Notifications to work, we must transfer your account details to our server(s) that handle Push. Our servers are very secure and we have never had any security issue, but this is of course not as secure as if your account details never leave the device. So if your company has special security guidelines, they may not want you using Push. But we think this will be rare as well. If your company has any concerns, they can contact us with any questions as well.