I'd recommend hiring a satellite phone for the trip. Once you get past Port Aransas there is no civilization until Matagorga - 80 miles, and if you break down on this stretch there is no vehicle traffic on Matagorda island and cell phone reception is patchy.
http://www.satellitephonestore.com/ is a good outfit that I've used twice.
Be careful at San Luis pass - give it a wide berth of at least a mile or two - there are some nasty sand bars lurking there.
Just north of Matagorda island there are some breakers marked on the chart. They get pretty big some times and have caught me unawares as they break 1/2 to 1 mile offshore.
Be safe,
Chris.