Thanks to a heads-up by Kay123, we now have news that Etisalat has extended its mobile internet plans to regular voice SIMs. From the Etisalat website:
Get the plan that’s right for you. Use with your regular etisalat prepaid SIM card or the Easynet data-only SIM card and Modem
The fixed plans that run on data-only SIMs are still available alongside the newly introduced packages.
Discuss this topic over at the MobilityNigeria Forum topic, Etisalat extends easynet to regular sims.