Yes. Analog telephones can be used with Press8's hosted PBX services.
An Analog Telephone Adapter (ATA) is required, such as the Lynksys SPA 2102 (see image below). This enables your analog telephone to be used on IP networks.
Keep in mind that if you use an analog phone you are going to be missing some features that you can only use on a VoIP phone like call transfer, conference calling, and DND (Do Not Disturb).
In Summary: Although you can use an ATA connected to your analog phone on a VoIP phone system, it is recommended that you instead use VoIP phones to get all the benefits and features.