Looking at Asterisk, asking for opinions

Currently my company is using 2 standard POTS lines for all calls. I’d like to go with Asterisk as our PBX solution as opposed to wasting money on an antiquated used system as others around here are pushing for. Overall the cost for the basic hardware is looking pretty cheap, but I need to come up with a proposal for cost of equipment and monthly cost. Obviously that is highly variable, but let me tell you our needs and maybe you can steer me in the right direction on where to look. Mostly this is related to telco service.

The goal is to be able to have multiple concurrent calls. We have a few people in the office and sometimes more than one needs to use the phone. Also, we’d like to have enough lines that we could have conference calls with 3-4 outside callers max. So I was thinking that we could get a 4 port FXO card and a couple more analog lines and feed them into the PBX, with one additional for fax.

Or we could look for a SIP provider. I’d like one that offers a flat rate unlimited plan. So we can budget for the year. I’ve been researching this and I assume someone offers this service, but I seem to be coming up dry. I need it to have 4 or so call in/out lines. I see many that offer additional DIDs, but it seems like they are just inbound only. Then maybe keep one additional analog line as a fail over (or not, is it worth it). We can’t afford to lease a PRI.

In short, is the 4 port FXO card + 5x analog lines monthly likely to cost more or less than going with a SIP provider? And any clue of some major SIP providers that offer multiple lines service for in and outbound calling with a flat rate?

You don’t say where you are located, and the choice of a SIP provider obviously depends on where you are (not much point in going for a US one if you are in Australia…)

If you are in US, I use ViaTalk (broadvoice.com) but I find ViaTalk much better than Broadvoice. As for the cost, it is likely that the SIP solution will be cheaper, but you might want to keep your analogue lines for fax and backup. If you are planning on multiple concurrent calls you need to be sure that your bandwidth is sufficient, and your router can prioritise VoIP traffic.