[Motorola Droid 4] highlandsun:
Still tinkering with this. Here are the system/lib files that the "GSM patch" archives update:

643696 Defl:N 318513 51% 2012-03-02 16:16 ea29f77b system/lib/lib-mot-lte-ril.so
13692 Defl:N 5635 59% 2012-03-02 16:16 5d586a83 system/lib/libmoto_nwif_ril.so
30368 Defl:N 12974 57% 2012-03-02 16:16 c41e8c74 system/lib/libmoto_qmi_ril.so
343424 Defl:N 176091 49% 2012-03-02 16:16 a86cca0f system/lib/libmoto_ril.so
5448 Defl:N 2010 63% 2012-03-02 16:16 f6df272b system/lib/libpppd_plugin-ril.so
22168 Defl:N 11992 46% 2012-03-02 16:16 18b182ce system/lib/libreference-ril.so
123664 Defl:N 57493 54% 2012-03-02 16:16 5f39940e system/lib/moto-ril-multimode.so

The libmoto_nwif_ril.so is identical to stock 215/219, so there's no need to update it. Same with libpppd_plugin-ril.so and libreference-ril.so. That leaves just 4 files that are different: lib-mot-lte-ril.so, libmoto_qmi_ril.so, libmoto_ril.so, and moto-ril-multimode.so. Of these 4, libmoto_ril.so and libmoto_qmi_ril.so are updated by the 219 patch. I kept the 219 version on my phone, and found that LTE wasn't working. So I copied over the 215 versions of lib-mot-lte-ril.so and moto-ril-multimode.so as well, and LTE is back again.

I still haven't actually tried GSM yet, still waiting for my micro-sim cutter to arrive in the mail. But after comparing build.prop files, this is what I've changed so far.

--- bprop.219	2012-04-28 12:18:46.060572850 -0700
+++ bprop2.219	2012-04-28 12:28:33.499485790 -0700
@@ -39,7 +39,8 @@
ro.sf.lcd_density=240
ro.default_usb_mode=2
ro.mot.ril.danlist=611,*611,#611
-persist.ril.ecclist=911,*911,#911
+persist.ril.ecclist=911,*911,#911,112
+# Use 2 for UMTS
persist.ril.modem.mode =1
# This defines the max event window manager can
# handle in 1 s. We may adjust this # for performance
@@ -67,7 +68,7 @@
# Time between scans in seconds. Keep it high to minimize battery drain.
# This only affects the case in which there are remembered access points,
# but none are in range.
-wifi.supplicant_scan_interval = 45
+wifi.supplicant_scan_interval = 90

# Indicate carrier OTA SP number schema
# refer to frameworks/base/telephony/java/com/android/
@@ -82,7 +83,7 @@
ro.opengles.version = 131072

# This is a high density device with more memory, so larger vm heaps for it.
-dalvik.vm.heapsize=42m
+dalvik.vm.heapsize=76m

# our HTML browser (not WAP browser ) does not need to specify UAProf URL
ro.mot.hw.uaprof=http://uaprof.vtext.com/mot/xt894/xt894.xml
@@ -140,7 +141,7 @@
#1 this is verizon wireless globle phone
#0 this is not verizon wireless globle phone
# NOTE: The definition moved to cdma_maserati.mk to support diff config for factory.
-ro.mot.phonemode.vzwglobalphone=0
+ro.mot.phonemode.vzwglobalphone=1
# END Motorola, nfjb73, 21-jun-2010, IKMAIN-732

# BEGIN Motorola, nfjb73 23-jun-2010, IKMAIN-624
@@ -153,7 +154,7 @@
# This is part of the VZW World-phone Feature. SMS are always sent to a US SMSC and then injected
# into that network. This allows for billing and give the user the impression that the device is
# still in the US.
-ro.telephony.gsm-routes-us-smsc = 1
+ro.telephony.gsm-routes-us-smsc = 0
# END Motorola, qmfd78, 14-Jul-2010, IKMAIN-884

# BEGIN Motorola, a22600 qmfd78, 16-Jul-2010, IKDROIDPRO-423
@@ -331,3 +332,12 @@
ro.build.version.full=Blur_Version.6.13.219.XT894.Verizon.en.US
ro.mot.hidden_keyboards=evfwd

+ro.ril.hsxpa=3
+ro.ril.gprsclass=12
+ro.ril.hep=1
+ro.ril.enable.dtm=1
+ro.ril.hsdpa.category=28
+ro.ril.enable.a53=1
+ro.ril.enable.3g.prefix=1
+ro.ril.hsupa.category=7
+