Wrong way round, the filters are for ADSL (broadband), you don't need them for dial-up.
What the filters do is filter the high frequency out from the analogues devices. The main line comes into the house and each and every analogue device, (phones, digiboxes, intruder alarms, faxes etc...), needs a filter between it and the incoming line.
As mentioned above, there are 2 ways of doing it, either at each individual point at which a device is plugged in or centrally at the NTE so all extension wiring after it is filtered, so thus all devices are filtered from a fixed unit rather than having loads of dangly bits everywhere.
The ADSL mosem doesn't need a filter and is connected directly to the incoming line. Most people use the filters to connect the ADSL modem to the line as it also incorporates the BT plug to RJ11 socket adaptor required for the RJ11 - RJ11 lead supplied with the modem. I usually make all my leads custom to the situation rather than usoing adapters.
If the ADSL modem is the only thing on the line then no filters are required.
EDIT: Having said that, there are 3 types of internet connection commonly used in the UK, dial-up, ADSL broadband and cable broadband.
The filters are to be used when ADSL broadband is supplied, i.e. broadband via a BT line.
They are not required when using dial-up or cable broadband as dial-up uses an analogue device, (modem), and cable broadband is supplied as a seperate service to the phone line.
The filters are used on ADSL as the different services are supplied over one pair of cables so different frequencies are used and the filters seperate these frequencies so that the ADSL doesn't affect the phones.
[quote author=scotspark link=1118664058/0#7 date=1118693250]broadband is adsl so the filters do apply
[/quote]
Technically not, broadband can be ADSL or cable.