The best replacement for call manager is call manager express.

The best alternatives to call manager are rated as following:
★★★★★  call manager express
★★★★  avaya
★★  asterisk
★  cisco call manager express

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Speaking about call manager, one probably shouldn't forget about tandberg.

Other search terms related to call manager and their ratings are:
★★★★★ tandberg
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call manager
call manager express
avaya