Sip Manager api support

Not all Android-powered devices support VOIP calls using SIP.

Even 2.3+ Android phones may not support SIP. This is not only a version issue. The final word is left to the manufacturer. Maybe it was too costly to add SIP support in the Ace.

SipDroid is based on another SipStack, which is why it can support Android 2.1. Sip stacks (Open source and proprietary) existed before the SIP Api in Android 2.3.

Edit: You can use an open source Sip stack like PjSip. It supports more versions and devices than the Android Sip stack.

All Android devices, which can connect to the Internet, support SIP.

After all SIP is just a protocol which requires connection to the Internet.

The traffic is divided in 2 major categories - SIP (SIP Messages) and Media (RTP Packages over TCP/UDP connection) - both require only access to IP Network and a SIP Server (strictly speaking you don't need Internet, if you have SIP Server in your local network).

In order to work with SIP, you need SIPStack implementation - doesn't matter if it's 3rd party or it comes from Android API (frankly speaking Android SIP API is very limited, for now). Check out this thread for a list of 3rd party SipStack implementations.

To answer to your questions:

Is there anything to be done to make it Sip supported?

Yes, you can use 3rd party SIPStack implementation.

How is Sip Droid working on 2.1 phone?

SipDroid uses MjSIP as SIPStack implementation, which is again, 3rd party SIPStack impl.