I have one pstn line with linksys spa3102 viop gateway with router with asterisk server , i use the pstn line for incoming and for making outgoing i use asterisk pbx. Issue is that i have to put welcome message for the company.
Using the Playback application. The details depend on the dialplan you are using, so you should ask the person, or organisation, that wrote it. In particular, if you are using a GUI front end, this is not the right place to ask.
Add a call of Playback at the appropriate point. The details depend on the existing dial plan. Unless you provide a copy, we cannot guess what that is.