1 PSTN (POTS) Line out, why bother with Dial Plan?

Hey,

I’ve almost completed my embedded Asterisk server and it seems to be working well so far with few problems.

My setup;

Neoware System
AMD Geode 300MHz CPU
256MB SDRAM
8GB Microdrive
Debian Etch Minimal install
Asterisk 1.2.13

Linksys SPA3102 - 1FXO/1FXS

1 PSTN Trunk
2 SIP Trunks

Okay so basically the two SIP Trunks are for incoming calls only and the PSTN for incoming and outgoings calls.

As the PSTN line is just our standard home line with no restrictions, I see no reason as to why I shouldn’t just do the following for my dial plan!

_X.

I’m guessing that as my Asterisk box is on the internet that I should not use this dial plan for security reasons, would this be correct? or am I safe?

Furthermore, how can I restrict dialing out to Internal LAN clients only?
Only thing I have set up is HTTP digest on my SPA3102.

Penny for ya thoughts!
Danny