You'll need to obtain the spec for building your own vSPC and integrating it with vSphere, contact VMware for the spec if you plan on building your own.
Here is a document that might help but it's around setting up a proxy for vSPC, but does contain some of the telnet sytnax strings - http://www.vmware.com/support/developer/vc-sdk/visdk41pubs/vsp41_usingproxy_virtual_serial_ports.pdf
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William Lam
VMware vExpert 2009,2010
VMware scripts and resources at:
Getting Started with the vMA (tips/tricks)
Getting Started with the vSphere SDK for Perl
VMware Code Central - Scripts/Sample code for Developers and Administrators
If you find this information useful, please award points for "correct" or "helpful".
At TDI Technologies (www.tditechnologies.com) we have made a very capiable Virtual Serial Port concentrator with all the necessary logging and reporting as well as alarming to meet compliance and security requirments. Yes, it is a commercial product and would love to show it to you. Even if you dont purchase it, you may get some great ideas on how to implement something like it.
Just a thought - why reinvent the wheel.
BEst Regards,
Bill Johnson
972 509 8511 office
I wrote a small open source vSPC server, vSPC.py, it may fit your needs: