Is it a T-1 video unit? If you are using PRI trunks in the switch, you can connect the video unit via another DS1 card in the definity. Configure the DS-1 as "line-side" to provide the timing to the video unit as if the PBX was the PSTN. Create a 23B + D PRI trunk group for the video T-1, dial "9" and the number and you should be in business. Using MCI and Sprint as the LD carrier for the voice PRI's shouldn't give you trouble. AT&T requires that their PRI's be registered with their "switched digital services" group. It will only work for about a week if don't register the BTN of the PRI. It's not a big deal, it just lets them charge you a higher rate for doing 64K digital data instead of voice. Any other LD provider besides the big 3 probably wont work since they'll reject the ISDN data setup messages on "voice" PRI's. For high volume applications, I would recommend the Adtran Atlas 550 or 800. You can tie the unit to the PBX or PSTN with a PRI or 2, then come off the Adtran with multiple PRI's, BRI's etc to support many oversubscribed PRI/T-1/BRI paltforms like fax servers, modem racks, VOIP, video, etc. without buying expensive dedicted Lucent DS-1 packs for each application.
-CL