Split VLANs for Voice and Data

[jag2050]

Hello Experts,

We have a centeralized network and 4 different sites and using MPLS on all the sites with CISCO STACKING, on each site we have 1 subnet i.e. site a IP 10.10.1.1 and on each site IP from 1 to 50 are for data users and 50 - 100 for telephones, using Default VLAN on all the sites.

We are now thinking to Split into 2 VLANS 1 for data and 2nd for telepnoes.
I am thinking leave the default vlan for data and create/add new vlan for telephones.

on all the sites IP are given by ISP i.e. site a 10.10.1.1 so to create a new vlan can I use same class of IP with different subnet i.e. 10.50.1.1..

Will you guys help me please where to start what things I need to look at and what type of configuration I need to compleate this task..Please..