H323 concurrent connections

Hello,We run asterisk as Voicemail server,How many people can connect to voicemail server at the same time using only H323 protocol?Now we use it and asteriks is not stable when h323 connection hits only 30 lines,its going down and asteriks must be restarted each time its happen and its happen too often.Any solution please?Maybe hardware configuration?now its 2.6 CPU,1Gb ram.We also did SIP test and its works better but not all the users able to originate SIP calls.

Thanks in advance