Need to send lots of SMS - should I use web gateway or SMSC / Telco ?

Hi

I'm based in UK.

I have a need to send lots of SMS messages.

I know there are some "web" based services which allow submission of SMS
(and subsequent "status" gathering .. i.e. "Message delivered to phone"
etc).

I wondered if anyone had any advice on whether to use one of these web
services, or whether I should go straight to what I think is called the
SMSC.

My understanding is that the telco's look after the SMSC's (true?)

When I went to Vodafone to ask tham about sending messages via their
server(s) , thay wanted to charge me 12p per message, whereas it seems the
web gateways only charge 7 p or sometimes as low as 4p .

Wondered if anyone had any thoughts / advice on why it should be that way ,
and what the best option is ?

Also - where can I find a complete list of gateways / telcos / smsc's
(whatever is relevant).

Many Thanks in anticipation

Mark