1. Start Zoiper application, then tap Settings | Accounts.
2. Tap Yes to pass.
3. Select Manual configuration.
4. Select SIP account.
5. Enter your account settings:
Account name: for example, MCN
Domain: SIP-domain address from registration email
User name: SIP ID
Password: SIP password
Auth Username: SIP ID
Tap Register to confirm changes.
6. Tap Network Settings and set parameters:
rport: Don't use
Enable STUN: disable
7. Turn on just a-law codec in section Audio codecs.
Also, if you have G729 codec, you can turn it on too.
Your application is ready to use!
In section Settings | Incoming calls you can enable Force Background to receive calls, when application is in background mode.
This settings are available in Zoiper 3.4 for iPhone and iOS 8.