3 OK plus
E1 uses TS16 as CAS channel (it uses 4 bits for line signalling). EuroISDN uses a 64K Dchannel. That means it´s the same in BW dedicated to signalling but protocols are a way too different. E1/T1 Register signalling is done by dual tones in each voice channel. See q.421 422& 424.
E1/T1 are digital systems as they transmits bits, but when you talk about voice, each sample represent tones or sounds. It’s clearer when you need to transmit data or fax over it. If you have E1/T1 every byte should be converted from/to a tone (Modem) If you have ISDN you need a Terminal Adapter and there is no Digital from/to Analog conversion.
Analog Call is done over a line to/from a home without ISDN (despite of being converted to digital in some parts of the Telco). You can set up analog lines in a PABX.
If you want to set up a Call Center you can get analog lines programmed as PBX, E1/T1, E1/T1 fractional (the same technology without all channels), PRIs. It depends on your switch and your provider.
What Cisco says it’s true for data calls (DDR or backup lines) but not for voice calls: You can call from an ISDN phone to a call center with T1/E1.