However, while discussions at IETF were stalled,  Reuters signed the first inter-service provider connectivity agreement on .  This agreement enabled AIM, ICQ and MSN Messenger users to talk with Reuters Messaging counterparts and vice-versa .  Following this, Microsoft, Yahoo! and AOL agreed to a deal in which Microsoft’s Live Communications Server 2005 users would also have the possibility to talk to public instant messaging users.  This deal established SIP/SIMPLE as a standard for protocol interoperability  and established a connectivity fee for accessing public instant messaging groups or services.  , Microsoft and Yahoo! announced that by the 3rd quarter of 2006 they would interoperate using SIP/SIMPLE,  which was followed, in , by the AOL and Google strategic partnership deal in which Google Talk users would be able to communicate with AIM and ICQ users provided they have an AIM account. 
- Combine the many disparate protocols inside the IM client application .
- Combine the many disparate protocols inside the IM server application. This approach moves the task of communicating with the other services to the server. Clients need not know or care about other IM protocols. For example, LCS 2005 Public IM Connectivity.  This approach is popular in XMPP servers;  however, the so-called transport projects suffer the same reverse engineering difficulties as any other project involved with closed protocols or formats. 
Some approaches allow organizations to deploy their own, private instant messaging network by enabling them to restrict access to the server (often with the IM network entirely behind their firewall ) and administer user permissions. Other corporate messaging systems allow registered users to also connect from outside the corporation LAN,  by using an encrypted, firewall-friendly, HTTPS-based protocol. Usually, a dedicated corporate IM server has several advantages, such as pre-populated contact lists, integrated authentication, and better security and privacy. 
Certain networks have made changes to prevent them from being used by such multi-network IM clients.  For example, Trillian had to release several revisions and patches  to allow its users to access the MSN, AOL, and Yahoo! networks, after changes were made to these networks.  The major IM providers usually cite the need for formal agreements, and security concerns as reasons for making these changes.
The use of proprietary protocols has meant that many instant messaging networks have been incompatible and users have been unable to reach users on other networks. This has cost the instant messaging format dearly.
Mobile instant messaging
Mobile instant messaging (MIM) is the technology that allows instant messaging services to be accessed from a portable device, ranging from standard mobile phones, to smartphones (e.g. devices using operating systems such as Android , Blackberry OS , iOS , Symbian OS , Windows Phone , et al.). It is done two ways:
- Embedded clients – tailored IM client for every specific device.
- Clientless platform – a browser-based application that does not need to download any software to the handset, and which enables all users and all devices from any network to connect to their Internet IM service, ideally. In practice, browser limits can pose problems.
In web browser
Gmail introduced instant messaging ability in its webpages, which can be used in a web browser with no need to download and install the IM client. Later, Yahoo and Hotmail also implemented this. eBuddy and Meebo websites offers instant messaging of different IM services. Generally such services are limited to text chat, although Gmail has voice and video abilities. As of , Gmail allows calling regular phones from their web-based IM client.