Some simple questions about SIPVOIP in general

Hi, some way when I start my iPhone-Softphone it is always already logged in into Voipbuster, but needs 5 seconds to log in onto my Asterisk server. Is there an obvious explanation?

Is there a good alternative for X-Lite that supports multiple accounts? I would’ve expected at least a decent GPL application.

Is Betamax the cheapest provider?

For PC or iPhone?
On Windows I’m using Zoiper Classic, on iPhone - iSip