Scholars have two opinions on touching Digital Quran
1) According to Imam Shurunbulali (Hanafi), The Quran is only touched and read only by those who are in the state of wudu. One cannot touch the Quranic verses in a mushaf of The Quran or inscribed anywhere else in isolation, eg. on walls, or coins (by extension on smart phones now).
2) According to Imam Ibn Abidin (Hanafi), if a Quranic verse is found written on a wall or coins, etc, it is permissible to touch it, however, it is not preferred.
Based on the second opinion one may read the Quran on smart phones without wudu although it is preferred to be in a state of wudu. One may take advantage of the blank areas between the ayaat to scroll on a smart phone.
Best Practice: To be always in the state of Wudu when reading The Quran (physical or virtual).
It is not necessary to be in the state of wudu to drink zam zam.
An extra point of benefit : Excellence of remaining in state of wudu at all time and praying 2 units of prayer (in non prohibited times) after completion of wudu with reference to the practice of Bilal r.a. Called tahiyyat-ul-wudu.