Installing a new system

I would probably not use 2.4 on something that size, wait a week or 2 and see if 2.6 levels out.

Thank you Jahyde. Actually I was waiting for 2.6. Finally, I thought maybe go with 2.4 is safer. I am using 2.4 from the time it's out and I don't have any problem with it. But I still have problems to setup 2.6 until now.

yea, basically sip is the way to go because its the most common.

You can use 2.4, even 2.2

I deployed a system over the summer with 2.0/2.2 that had 160 Hard Desk Linksys SPA942 Phones, and 200 DIDs... on a dell poweredge.

Trixbox is ready for primetime now... your server is capable.
Theres no need to wait to deploy, except to assemble the hardware, and hopefully by then 2.6 will be kinkless.

So if youre set to go, then go; the software is ready and can easily handle a large deployment.
Id even call yours med-large; not a full large.

Unfortunately there aren't really any general rules. Every installation is different and what works well for me may be the worst option for you.

That being said: SIP phones are more readily available at the moment, NAT issues are surmountable (if a bit daunting the first few times) and mostly the IAX phones available are of questionable quality. So, yeah, as far as phones are concerned, SIP is "better" for the time being.

However, there's nothing stopping you from doing what you want and if it works for you then that's great.

I strongly urge you to buy a small selection of sample phones and try them out before you make your main purchase. Alternately, find someone in your area that has some and is willing to have you give them a once over. The last thing you want to do is buy 100 phones and find out all your users hate them, or that the configuration is a nightmare or whatever.