@g3uiss:
Yes, the land line migration does seem to cause complications when changing ISP's.
My daughter migrated FTTC & phone with Plusnet to FTTP with BT dropping the land line last month, no issues, all went fully to plan on the day.
Once I manage to get everything cancelled with BT I will attempt to get a comparably priced deal from Zen for FTTP & phone, at least with the one ISP there should be much less chance of loosing the existing service before the new service is in place or indeed the long standing LL number.
@atkinsong:
Yes, may have to consider the 2 step migration process as outlined, will see if Zen can offer the simpler alternative first.