Here are descriptions of the more relevant changes in EVSS 3.4

PrivateGSM changes

The main change is full and certified support for IOS-7

No other major changes or features are present

PrivateServer changes

Nexmo SMS support

Support for Nexmo SMS gateway: easy and affordable SMS delivery, even to US phones numbers, with no setup costs. 

SIP trunks management

Trunks configuration can be immediately tested and their status is reported in realtime by web console.

Secure SIP trunks

This version or PrivateServer carries full support for secure SIP trunks. It is now possible to configure trunks to use SIP over TLS and SRTP to fully encrypt calls between PrivateServer and other PBX, such as Cisco Unified Communications Manager.

In case of secure trunks, it is possible reject insecure calls playing a message to users that will be warned about the security issue

BES 4.x support

Before this version, Blackberry devices connected to BES 4.x could not complete automatic activation, due to a strange strange SSL negotiation done by Java 5 application, such as BES 4.1.

Despite SSLv2 is disabled, PrivateServer can now accept SSLv2Hello message, used to negotiate SSLv3 and TLS1.0 connections.

More details at RIM website