Какое время сюда нужно вставить?
Yes, I guess so. Do you know what … (you / do) this time next Sunday?
....(I/get) ready to go to London.
OK.So, ....(I/phone) about three o'clock next Sunday.
Great. .....(I/wait) for your call

Will you ready to go London? = Там нет вопроса, нужно повествовательное предложение. Не буду вчитываться в смысл, может быть I am ready to go to London.

Do you know what will you de this time next Sunday? Will you ready to go London? So, I will phone about three o'clock next Sunday. Great.I will wait for your call. (Future Simple)