Complex sentence: In 2001, the same Mobitex network proved to be effective in communications relay in Manhattan during the September 11,2001 terrorist attacks especially after most cellular and wireless telecommunicaitons services were knocked-out or overloaded in New York City.
Split into simpler sentences: In 2001, the company's Mobitex network proved to be effective in communications in Manhattan during the September 11,2001 terrorist attacks. Most other cellular and wireless telecommunications services were knocked-out or overloaded in New York City.