No. Once the plan has commenced and you have started using your service, no changes can be made, as stated in your Customer Contract (Terms & Conditions). Both Data-Only and Voice/SMs SIMs are different products that cannot be interchanged later.
You will need to purchase a new SIM from us and cancel the plan on the existing SIM. It is important to note that we will not provide any refunds or pro-rated adjustments for any unused Data on your Existing SIM.
If you have already paid for an Annual Plan, we can assist you with transferring your existing contract to another individual. It is important to note that you are still liable for any amounts due on your Annual plan (such as Addon purchases or overage charges) prior to the transfer being completed.