Doesn't make sense to me, a Gatekeeper is an H.323 entity. Perhaps what you heard was related to Call Manager, which support sip endpoints since version 5
You need something in the middle to perform translations, may be builtin...check this RFC 4123 (RFC4123)
Getting Started
Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: