Samsung Galaxy S2 drops carrier network
I have had the exact same problem.  CyanogenMod SGS2, baseband I9100XXKE7, checksum 163ecafa01912637fe344ec1f8264d70.  The only difference is I'm with Optus in Australia.

After extensive research, the solution I found was simply a matter of identifying an appropriate Modem+RIL (Radio Interface Layer) to install.  I'm still looking for an appropriate one for me, although I9100XXLS9 has stopped the dropouts, it won't let me make calls.

Unfortunately it seems the best Modem+RIL combo is very dependent on your carrier+phone combo.  I found a discussion about various RILs to use for SGS2 in New Zealand.  You may find what you're looking for there.  I've seen people discussing I9100JJLS2, I9100XXLS8 and I9100PBVLP7 as good modems.

If you look at your other question (How to manually replace ones RIL) you'll see it's pretty quick and easy to flip around between different RILs when you know what you're doing.  Give them a try and see how you go.