If you would like to receive free voicemail  messages at little or no cost to set up.

www.lycamobile.co.uk offer them .Minimum top up is £5.

You need to use it occassionaly.If you do not use your SIM Card to make a voice call, or send a message or data, or if you do not purchase a top-up using the Top-Up Services, for a period of ninety (90) days from the date you registered or activated your Account or your last use of the Services (whichever is later), Lycamobile will contact you by SMS or e-mail advising you that your SIM Card will be deactivated. Lycamobile will then provide you with an additional thirty (30) days to make a voice call, send a message or data, or purchase a top-up using the Top-Up Services.

Also their is www.sipgate.co.uk you can get a free geographical 01/02 number, set it up to go voicemail, and it will email you messages.No credit required.

White Mobile also offer Free Voicemail https://www.whitemobile.com/white-mobile-rates/ plus good rates for UK Calls.

Note they will disconnect your SIM if during the previous 60 days you have not Registered a new Top Up or you have not made chargeable calls from your SIM. For the avoidance of doubt calls shall include but not be limited to voice calls, data calls and text messaging.