Mears will pick up at Disney resorts, and Disney will help (in a small way).
Dial "0" from your Disney resort phone the night before you wish to go to Universal/IOA/Sea World. When the operator answers, ask to be transferred to Mears. (That is how Disney will help, save you the 75 cents to dial Mears directly).
When Mears picks up the line, tell them you wish to go to Universal/IOA/Sea World in the morning, approximately what time and what resort you are at.
They will give you a pickup time and place.
Be at the pickup place 15 minutes before they state.
When the van/bus arrives pay the driver $15 pp RT in CASH. (I also usually tip the driver $1 PP per way.)
You will then be taken to Universal. You may also stop at other resorts.
When you arrive at Universal, you can either arrange a pickup time at that time, or on the return voucher there is phone # you can call 2 hours before you wish to go back to your resort.
They will tell you a pickup time.
Return to where you were dropped off. Give the driver the return voucher and board the bus/van. You will be transported back to your resort. There may be other stops before you get to your resort.
If you know in advance you wish to use this service and want to pay with a credit card, you can purchase a Round Trip Voucher at the Mears desk at the airport with a credit card. You still need to make the actual pickup reservations the night before.