The next is a study i did over the market requirements for "Systems Engineer" in my country in Southamerica:
SAP, Web development, google tools, databases, SQL, webmasters, DB Oracle ,Networking WAN, LAN, VoIP, SS7, Open Source, 2g,3g,gsm,UMTS, AAA, SMSC, Process (Ps , prstat, vmstat, sar)...