I'm completely new to VoIP and the likes, and I'm trying to find information about what could be the best setup for this.

I need 4 (maybe more in the future, but maximum 5 or 6) wireless extensions, connected to 1 PSTN line, and maybe 2 in the future. I've been trying to gather information about the gear needed but everything I find seems too much over-the-top (and extremely expensive).

The main problem is that the physical place we are on doesn't have possibilities of having a decent internet connection, so using a external VoIP "virtual PBX" is not an option.

Thing is, even if small, phone is critical to this organization.

I currently have an analog DECT/GAP PBX which does what I need, however the PBX is very bad and the call quality is horrible, and that's why I want to change it.

The requirements would be:

• 4 wireless terminals (routing cable is not an option), all of them ringing on incoming PSTN calls.
• Ability to do internal calls (4 separate offices) and ability to pass calls between terminals.
• The 4 terminals should be able to access the external PSTN line without dialing any special codes.
• Very important: terminals should be able to issue commands on the PSTN line to the external operator in the form *nn*nnnnnnnn# . Don't know wether this could face to be a problem, but I've had problems with analog PBX which would take any * as a PBX command and wouldn't allow terminals to send it to the external lines.
• Not so important, but would be nice to have: call waiting music

Could anyone recommend such a setup? I need to be able to do this on a EXTREMELY LIMITED budget (that is: I don't have a limit, but all should get as much to zero as possible).

I have enough spare powerful computers and a 300mbps wireless network which works just fine, so that's not to include in the budget.

Don't really know if this is the best place to ask, but it's the most StackExchange-related site I've found to this subject.