Paging to 7921

Hello, new to all this but here goes. We have a customer who requires the ability to be able to receive paging on 7921 handsets. It does work but is very jittery. Sounds like packet loss. We have upgraded the UC to 4.2.7 and the 7921 to 1.1.1 it improved slightly but still not audible. Has anyone tried this? Anyone got this working. Any help or hints much appreciated.