You must have EDGE for VV to work. BTW. Post this is Technical for a better response
For clarity I live in a non edge area and still get Visual voice mail. I do get the error sometimes but only lasts an hour or so.
iPhone 11 Pro 256gb on unlimited data iPad Pro 12.9” 2020 256gb refresh o2 family discount Apple Watch series 4 My first mobile was in 1995 a CM-R111 from sony on Cellnet. Wincanton South Somerset (Full 4g 3G 2g indoor coverage) Remember we are all customers here not customer services