Hi! first we have to separate that into parts and TLAs:
MWI (message waiting indication), the light that says you have VM
BLF (busy lamp field), the light that lights up when other EXTENSIONS are in use.
You want phones that do both of these: Try SNOM 360, AAstra 9133i/480i, or if you are really budget conscious, Grandstream GXP-2000. If the phones only need one SIP line and don’t need Power over Ethernet (so they DO need a wall wart adapter), try the AAstra 9112i. AAstra hardware is highly recommended, very good quality and easy to remote configure via tftp. Snom is great too. Grandstream is harder to configure and not as solid feeling.
For the real bottom of the barrel look @ Grandstream BT100 series. They look and feel like cheap plastic toys, have no caller id with name, and no BLF. MWI is accomplished by flashing its backlight, no real MWI LED. However they are very cheap ($50 or so, probably less in quantity).
The web panel you want is called FOP, the Flash Operators Panel. It’s written in flash and may be exactly what you want.
Not sure what tigernet phones you are talking about. Post a link? If you are talking about the Tiger Jet voice modems aka knockoff Digium X100 cards, stay away from those. They are not reliable. I recommend a Digium TDMxx or Sangoma A200 type card, many have used these with excellent results.
That all said,
for phones it depends on what wiring you have now. You said this is low budget… If you have ethernet everywhere (especially if its 802.3af powered) then a handful of AAstra 9133’s would be just what you need. Grandstream 2000’s are a bit easier on the wallet but harder to remote configure.
Another option- if the building is not wired for Ethernet or already has analog phone wiring, give the kiddies analog phones, or make them bring their own.
Use either a channel bank (t1 card and t1 to many analog device, or xorcom makes a USB channel bank that doesn’t need a T1 card and apparently works great) or a high density card (Digium TDM2400 analog card or something similar).
The advantage to going analog would be less valuable equipment in student posession, if they destroy a $10 slimline style analog phone that’s alot better than a $50-150 IP phone. I guess that depends on your building infrastructure and how well behaved your students are.
As for lines, what you could try is just a wholesale company. There are a number of companies that will charge you about 1-3cents/minute for calling anywhere in the USA/canada/etc, and you can set up as many calls as you want. They will also sell you DIDs (phone numbers) which will go into your system via VoIP and you can have * do whatever with them (including mapping them 1 to 1 to dorm phones).
This could be supplemented with a few analog phone lines for local calls. * could be set up so 4 digit extensions call locally only, 7 digit number go out over analog and 11 digit (1-xxx) goes out over VoIP.
Hope that helps!