A trend appears to have developed were ISP's try to get you to use their own VOIP system as well as their broadband and then some also try to get you to use their mobile service as well in one linked package so that it is much harder to leave them as you end up looking all three services; broadband, VOIP and mobile when you change ISP.
Personally, I concluded that is better to use separate broadband, VOIP and mobile providers as when you change any one of the three the other two stay as you were until you move them and you are also not locked into using the router that was supplied by the ISP.
Vodafone appear to give you a phone number weather you want it or not and I suspect the best way to find out about another phone line with Vodafone would be to ring them.
I suspect that it would be better for you to have two VOIP lines with a dedicated VOIP provider for the flexiblity to change providers for the reasons outlined above.
There are a number of threads, on this board, regarding VOIP Providers and that is down to personal choice: personally, (since Sipgate Starters future for 2023 is uncertain), I presently have two VOIP lines, (one with Sipgate Starter and one with Voipify), both of these lines use one Gigaset N300A base station and four Gigaset C575A phones. - As I recall the Gigaset N300A Base Station can cope with over four separate lines from the same of from different VOIP providers.
I am curious as to why you chose Vodafone for broadband because even though they are cheap, (They advertise 900 mbps for £40 per month), apparantly the speeds are really slow and they have some very poor reviews regarding line speed.
Kindly advise us, (on the Vodafone Board), how you find Vodafone as an ISP.
Regards,
Fido
Zen 900 mbps FTTP