Initial setup experience & questions

Received Grandstream today. Did not come with any directions or a phone number printed anywhere. No documentation at all.

Plugged phone in behind router (WRT 540G2). Did not make any change to my router such as port forwarding or static IP. (Don't know how to configure Grandstream). I plugged the CAT 5 cable from one of my ports on the router to the Grandstream WAN plug. (Assume this is correct).

Plugged phone in. All seems to work for the most part. Some issues I encountered.
a) When calling my land line phone at home. Some phones could take the call, others could not. One of my land line cordless phones seemed to disconnect the call. Putting a DSL on that base station fixed the problem.
b) It seems the first time I call a number, the call disconnects within one second of the call being answered. All additional calls go through. Experienced this with two numbers so far, so may be a coincidence. Maybe the same problem noted in “call>pickup>hangup?”

So my questions are:

1) I want to keep the Grandstream behind the router. Do I need to set up port forwarding to a static IP since phone seems to be working so far? How do I configure the Grandstream's IP as recommended by some?
2) Can I connect Grandstream to an external answer machine?
3) How do I use all the features VOIPO offer such as e-mail messages, vpanel, voicemail, SMS notification, ect...

Any assistance or advise is appreciated.

Just a follow-up, called tech support, received an e-mail with a vpanel password. Most questions were answered as I previewed options.

One last question: My GS is behind a router. I did not port forward, I did not assign static IP yet. So far no problems. Should I leave well enough alone or is some other problem looming?

I would do both, as well as disabling SIP ALG.

You don't really want the IP address of your GS changing, as that can only cause issues. I would port forward as well, as you don't want anything sent back and forth on those ports clipped for any reason. While you at it, you probably want to disable SIP ALG as well.

Just my opinion, and I'm no VOIP or TCP/IP expert, nor do I play one on TV.