I had a topic (which unsurprisingly was very quiet) asking for help using a DUN enabled phone as a 3g dongle. After a lot of testing and whatnot, I come up with a working solution and other neat information.

First off my setup;

Acer Iconia A500; Running Thor v14.2 ROM
Build.prop mod installed from here; http://forum.tegraowners.com/viewtopic.php?f=9&t=71
Phone; LG EnV2 Verizon prepaid.

Solution should work for any tether enabled verizon phone, POSSIBLY Verizon Dongles, and other brands of phones besides LG.
This guide assumes you either have, or know how to flash Thor's rom, and other flashable zips. I will not provide ADB instructions, but if someone would like to send me instructables how; I will add them into this post.

From a 'fresh' or unmodified version of Thor's ROM (I used v14.2 [url=http://www.tegraowners.com/?p=1272]Available here[/url]), follow the build.prop install instructions in the link above.

Then using root explorer (or equivalent root browser) [b][color=#00BF00]remount /system rewritable[/color][/b] and open the build.prop file in a text editor.
Comment out ro.carrier=wifi-only and uncomment the rest of the block. It should match the following when done;

[color=#00BF00]#ro.carrier=wifi-only
picasso.3g=true
rild.libpath=/system/lib/libhuawei-ril.so
rild.libargs=-d /dev/ttyUSB2
ro.pad.features.modem=true[/color]

Save the file and check permissions; they should still be [color=#00BF00]rw-r--r--[/color] and reboot the tablet.

This enables the 3g menus, and using the previous build.prop, lets your A500 read as an A500 instead of an EPAD.
Note: You DO NOT need to set an APN, Verizon, being a CDMA network, does not use APNs. The 'login' information is in the phone itself. It just needs the commands to initiate a data connection.

Now is where it got tricky to figure out;  If you open a terminal emulator as root (type [color=#00BF00]su[/color] at the prompt) and type [color=#00BF00]ppp-start.sh[/color] you will get a couple of lines with this error;

[color=#FF0000]pppd: In file /system/etc/ppp/peers/3g: unrecognized option '/dev/ttyUSB2'[/color]

or similar.

In the terminal prompt, type [color=#00BF00]dmesg | grep tty[/color] it will return several lines, I noticed I had a device on [color=#00BF00]ttyUSB0[/color] not ttyUSB2.
On study, some modems make several ports for control, monitoring, etc. mostly data connections are on ttyUSB2, which is my guess why it was default.

I figured out by editing the ppp config file that ttyUSB0 wouldn't error, but wouldn't start either. I looked back at the grep and noticed something else that matched and I had seen before in my studies; [color=#00BF00]ttyAMC0[/color]

So using the same method as editing build.prop, edit [color=#00BF00]/system/etc/ppp/peers/3g[/color] it should read as follows;

[color=#00BF00]ttyACM0
921600
crtscts
defaultroute
modem
noauth
noipdefault
persist
updetach
usepeerdns
connect 'chat "" AT OK ATD#777 CONNECT'[/color]

Note the ttyUSB2 being changed to ttyACM0, apparently the data serial for the phone, and atd number being changed to #777, Verizon's 3g number. (Speculation that you could increase the 921600 for higher USB bus speed, but I've not tested this).

Save the file and confirm the permissions are; [color=#00BF00]r-xr-xr-x[/color]

Open terminal emulator with root permissions and again try [color=#00BF00]ppp-start.sh[/color]
This time after it says pppd, after about 5 or so seconds, it should list your IP and other information confirming the connection.  You should see TX and RX packet info on the phone screen. If so, congrats you are now connected via 3g with the phone.
To turn off the connection, use the command [color=#00BF00]ppp-stop.sh[/color] I suggest making a couple script manager widgets to 'shortcut' these.
Note; [color=#00BF00]If the screen turns off, the phone will disconnect and you will have to unplug the phone, restart the ril daemon, plug the phone back in, and run ppp-start.sh again.[/color]
You can install the [url=http://android.upce.cz/acer/ril-daemon_restarter.apk]ril-daemon-restarter[/url] to easily restart ril, or in terminal emulator; stop ril-daemon then start ril-daemon
(I found the ril-restarter in one of thor's comments [url=http://www.tegraowners.com/?p=1188]here[/url] and suspected credit goes to dmatusek76 on XDA.)

Things that I've tested; 
[color=#00BF00]Browser works despite saying 'no connection' at the start.[/color]
[color=#00BF00]Market can browse apps,[/color] [color=#FF0000]but not download them.[/color]
[color=#00BF00]GMail seems to receive,[/color] [color=#FF0000]but not send emails.[/color]
[color=#00BF00][u][b]Netflix works.[/b][/u][/color]

Best part; [color=#00BF00]The Portable Wireless Hotspot option in Settings > Wireless & Networks > Tethering & Portable Hotspot menu[/color] [u][b][i][color=#00FFFF]works[/color][/i][/b][/u] [color=#00BF00]to create a 3g Wi-Fi hotspot.[/color]
All connections through the hotspot are [color=#00BF00]NOT BLOCKED[/color]; i.e. using my android to connect to the tablet, I was able to browse apps, download them, send emails, etc. 

My theory on the reason the tablet won't; Some apps (like Google Voice and AndroIRC), check for an internet connection BEFORE TRYING, and if it isn't 'available' it just gives you a warning and stops without actually TRYING. Other apps just try to access the internet without checking for a connection first (Like Netflix), and they work. 
This theory is backed up by the Browser first checking for a connection (hence the 'no connection available' popup), but then loading as it continues to try anyway after the check.
Using the wireless hotspot, the phone sees it as a full connection, so nothing stops during the 'network check'.

I hope this information might be useful in getting other devices, phones, dongles, etc. working with this masterful tablet.
Please let me know if it works and if you use other equipment. :)

Credits; 
Thor for his awesome rom that supports USB 3g in the first place
pimpmaneaton for the build.prop