The company may have something in place for remote access. If not, then there must be ways for you to email or courier files/information back to the office.
The company may subscribe to an online collaboration program that allows remote workers to meet and share work.
In many cases, employees use their own computer equipment, but the company provides copies of software programs which are used onsite.
During discussion of the remote work arrangement, it should be made clear who will be responsible for providing the equipment and tools needed. This includes who is responsible for phone charges - local and long distance.
More companies are considering the use of company owned mobile gear so that they retain ownership and more control of the data contained in the mobile gear. If employees use personal mobile gear, then leave a company - that company has no way to know 100% that any critical information has been deleted and will not be used against them.