Engaging patients in a group-based weight loss program is a challenge for the acute-care hospital outpatient setting. To evaluate the feasibility, effectiveness and cost-effectiveness of a telephone-based weight loss service and an existing face-to-face, group-based service a non-randomised, two-arm feasibility trial was used. Patients who declined a two-month existing outpatient group-based program were offered a six-month research-based telephone program. Outcomes were assessed at baseline, two months (both groups) and six months (telephone program only) using paired t tests and linear regression models. Cost per healthy life year gained was calculated for both programs. The telephone program achieved significant weight loss (-4.1 ± 5.0 %; p = 0.001) for completers (n = 35; 57 % of enrolees) at six months. Compared to the group-based program (n = 33 completers; 66 %), the telephone program was associated with greater weight loss (mean difference [95%CI] -2.0 % [-3.4, -0.6]; p = 0.007) at two months. The cost per healthy life year gained was $33,000 and $85,000, for the telephone and group program, respectively. Telephone-delivered weight management services may be effective and cost-effective within an acute-care hospital setting, likely more so than usual (group-based) care.