Standard Vonage service is locked to the ATA they send you. It is not possible to connect Asterisk (or any other SIP UA) directly to your standard Vonage service.

Quoth their TOS:
" c. Unauthorized Usage

Customer may not program the Number into any equipment or
infrastructure in or on which the number is intended or used as the
origination or destination of a communication other than the Device
that was provided by Vonage."

However Vonage does sell an addon service called Vonage Softphone: for an extra $10/mo you get assigned a second DID with 500 outgoing minutes, and you get the SIP credentials as well as a copy of XTen's X-Pro softphone. To get this you must also be a normal Vonage subscriber, with at least one line going through the ATA. This will work with Asterisk, but it is more expensive.

By far the most elegant way to connect an Asterisk server to Vonage is through a Vonage Business Plus account. The Vonage Business Plus program is designed to allow business customers to connect SIP gateways and IP PBX directly to the Vonage network. Plans range from 4 DIDs with 5K minutes for $149/mo. to 24 DIDs with 50K minutes for $999/mo. Incoming calls are free and DIDs can support multiple channels. As with all Vonage accounts, calls within the Vonage network are free.

If you do happen to be using a Vonage adapter through a TDM card and want the the called id name to show on your SIP phone here is how to do it:

exten => s,1,Cut(newcidname=CALLERID,\",3)
exten => s,2,DBPut(cidname/${CALLERIDNUM}=${newcidname})
exten => s,3,LookupCIDName

Basically take what Vonage does send down as callerid and split it up by the " marks and then set it in the local db and then call the lookup to set CALLERIDNAME for you since you can't set it manually.

PLZCONFIRM: The newer version of the Cisco ATAs firmware do not require this patch to pass caller id.

How to configure Asterisk to work without a Vonage ATA

NOTE: You must have a Vonage Softphone or Vonage Business Plus account for this to work.

By: Neel - neel_007
Vonage <---> Asterisk Complete Config
2005-02-24 20:18
Hello Asterisk Users,

After Brain storming for couple of hours, days, and weeks, finally got Asterisk to work with Vonage for Inbound and Outbound calls.

Requirement: -

1. Vonage Softphone account
2. Asterisk
3. Couple of SIP Phones

Here is my sip.conf

[general] 
port = 5060 ; Port to bind to (SIP is 5060) 
bindaddr = <<Local IP>> ; Address to bind to (all addresses on machine) 
context=incoming 
disallow=all 
allow=ulaw 
allow=alaw 
allow=g729 
allow=g723 
externip=<<External IP>> 
localnet=<<Local IP>> 
localmask=<<Local mask>> 
nat=yes 
register=<<VonageDID>>:password@sphone.vopr.vonage.net:5061/202 
[vonage-out] 
username=<<VonageDID>> 
type=friend 
secret=<<password>> 
port=5061 
nat=yes 
host=sphone.vopr.vonage.net 
fromuser=<<VonageDID>> 
fromdomain=sphone.vopr.vonage.net 
dtmfmode=rfc2833 
auth=md5 
[vonage202] 
username=<<VonageDID>> 
type=friend 
secret=<<password>> 
port=5061 
nat=yes 
insecure=port,invite
host=sphone.vopr.vonage.net 
fromuser=<<VonageDID>> 
fromdomain=sphone.vopr.vonage.net 
dtmfmode=inband 
context=from-pstn 
canreinvite=no 
auth=md5 

Here is my extension.conf

[ext-did] 
exten => <<VonageDID>,1,Goto(ext-local,202,1)  
or  
exten => <<VonageDID>>,1,Goto(aa_1,s,1) If you are sending the call to IVR. ...